feat(web): add and enable auto-correction 📚

[jahorton]

This establishes something I've been waiting a long time to enable: when one prediction is sufficiently more likely than all alternatives, it will be automatically selected for application when tapping the space bar. In short: auto-correct.

Current conditions for auto-correct:

• The pre-existing prefix for the correction/prediction is not zero-length. (We don't want to auto-select 'the' from an empty string with SIL EuroLatin, after all.)
• Any "correction" applied to generate the suggestion must be the highest-probability correction that leads to a valid suggestion.
  • It doesn't have to be the most likely keystroke - just the most likely keystroke that can reasonably produce a word from the model.
• The suggestion to be auto-selected must have at least twice the probability of all other generated suggestions.
  • I started off with a harsher threshold, but auto-selection was pretty rare then. It could probably be more aggressive... but that does raise the risk of false positives.
  • This is not part-of-speech aware in any sense - if "book" and "books" are about as likely as each other, "boo" would not auto-select either "book" or "books"; neither would win, even if they were the only words in the model, as there's no clear probability winner.

These conditions may, of course, be further tweaked... but this seemed to be a reasonable initial set to use for testing.

One interaction that should probably be reviewed for correctness + user-friendliness: While the banner is receiving any mouse-based or touch-based interaction, the auto-selected suggestion will be deselected - even if just to scroll before releasing the banner. If it was a scrolling interaction, the original auto-selected suggestion will be reselected and rehighlighted. If a suggestion was applied, however, there will be no reselection or re-highlighting.

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Notes for review:

This PR's changes utilize existing plumbing that was prepared all the way back with #1747 during 12.0-alpha. We prevented it from actually auto-applying anything at the time, but most of the design work was done back then.

#3702 was added a while back in order to swallow a single whitespace tap after applying a suggestion via banner UI. We wish to maintain that here. However, we don't swallow the whitespace after application if it was triggered by pressing the spacebar... because we'd have already tapped the spacebar once.

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User Testing

TEST_LOOK_AND_FEEL: Using Keyman for Android, play around with predictive text and report back on how the interactions feel.

• When it presents an automatically-selected suggestion, do banner interactions feel intuitive?
  • Be sure to try scrolling the banner when testing this.
  • As might be noticed by the recording above, I find tempta to be a good "prompt" input for this. Do try others, though.
  • Do you see any banner "flicker" during these interactions? Things should feel as smooth as they usually do.
• When it presents an automatically-selected suggestion, do keyboard interactions feel intuitive?
  • Just in case, be sure to hit the spacebar at least twice in a row when an automatically-selected suggestion is selected (before the first tap).
  • Also, try selecting a different suggestion from the banner, then tapping spacebar.
  • Also, try selecting the auto-selected suggestion from the banner, then tapping spacebar.
• If the answer to either question above is "no", FAIL the test and report what felt wrong.
• Do NOT fail this test if you expect something to be automatically selected, but it isn't.
• ... but DO fail this test if a suggestion isn't auto-selected when it's the only one available.

TEST_POST_APPLY_WHITESPACE: Using Keyman for Android...

• With an auto-selected suggestion available, press the spacebar twice in a row.
  • There should be a total of two spaces after the applied suggestion.
• With an auto-selected suggestion available, press the suggestion, then tap the spacebar twice in a row.
  • There should be a total of two spaces after the applied suggestion.

TEST_POST_APPLY_BACKSPACE: Using Keyman for Android...

• With an auto-selected suggestion available, press the spacebar to apply it.
• Then, press backspace.
• You should see a "suggestion" that restores the word as it was before you applied the suggestion.
  • The "suggestion" should not be auto-selected.

[keymanapp-test-bot]

User Test Results

Test specification and instructions

• ✅ TEST_LOOK_AND_FEEL (PASSED): I tested this issue with the attached "Keyman-18.0.60-alpha-test-11866" build on the Android 14 Physical devices. Here, I have given my observation. (notes)
• ✅ TEST_POST_APPLY_WHITESPACE (PASSED) (notes)
• ✅ TEST_POST_APPLY_BACKSPACE (PASSED) (notes)

Test Artifacts

• Android
  • Keyman for Android apk
  • FirstVoices for Android 16.0 apk
  • FirstVoices Keyboards for Android apk
  • KeyboardHarness apk
  • Keyman for Android 16.0 apk
  • KMSample1 apk
  • KMSample2 apk
• Developer
  • Keyman Developer
  • Compiler Regression Tests
  • kmcomp.zip
• iOS
  • Keyman for iOS (simulator image)
  • FirstVoices Keyboards for iOS (simulator image)
  • TestFlight internal PR build version - 18.0.60 (0.11866.11395)
• Keyboards
  • Test Keyboards
• Web
  • KeymanWeb Test Home
• Windows
  • Keyman for Windows
  • FirstVoices Keyboards for Windows
  • Text Editor (32 bit)
  • Text Editor (64 bit)

[jahorton]

Potential followup:

Note that this method does not actually reference anything in the class. We could make it static... or even better, we could make it a standalone method.

Why this point is significant: it's isolated in a manner great for unit testing. No need to mock inputs or anything! I haven't actually defined any unit tests for it yet, though.

... I'd be more proactive about unit testing this if the effects weren't already easy to see during actual KMW use.

[mcdurdin]

I think the unit test is probably a good idea for future maintenance.

[dinakaranr]

Test Results

• TEST_LOOK_AND_FEEL (PASSED): I tested this issue with the attached "Keyman-18.0.60-alpha-test-11866" build on the Android 14 Physical devices. Here, I have given my observation.

1. Installed the "Keyman-18.0.60.apk" file and gave all permissions to the application.
2. Checked the "Enable Keyman as system-wide keyboard" and set the keyboard as the default keyboard box on the settings page.
3. Open the Keyman app. Enable the "Predictions" and install the "Dictionary."
4. Added a sentence to the notepad. 
   Results:
   Enter a word, and it will be observed that the word is highlighted on the banner.
   Verify that I can scroll the banner words. 
   Auto-suggestion and auto-correction feature work after pressing the "spacebar" key.
   There is no flicker on the banner while selecting the word.

• TEST_POST_APPLY_WHITESPACE (PASSED): 

1. Installed the "Keyman-18.0.60.apk" file and gave all permissions to the application.
2. checked the "Enable Keyman as system-wide keyboard" and set the keyboard as the default keyboard box on the settings page.
3. Open the Keyman app. Enable the "Predictions" and install the "Dictionary."
4. Added a sentence to the notepad.
5. Enter a word and the observed that the word is highlighted on the banner. 
6. Press the "space bar" two times.
   Results: Here, The word is added. Two spaces appeared after the word.

• TEST_POST_APPLY_BACKSPACE (PASSED): 

1. Installed the "Keyman-18.0.60.apk" file and gave all permissions to the application.
2. Checked the "Enable Keyman as system-wide keyboard" and set the keyboard as the default keyboard box on the settings page.
3. Open the Keyman app. Enable the "Predictions" and install the "Dictionary."
4. Added a sentence to the notepad.
5. Enter a word and observe that the word is highlighted on the banner. 
6. Press the "Spacebar" for two times, and then press the "Backspace" key.
   Results: The suggestion word appeared in the double quotes, and it is not auto-selected. 
   This feature feels good and works well. Thank you.