Fix legacy implementations

[daohoangson]

This PR is running in parallel with daohoangson/flutter-tinhte_demo#224 to document the migration steps required to upgrade an existing app to next.

[github-actions]

Demo app

b8b1d81 APKs:

• app-armeabi-v7a-release.apk
• app-arm64-v8a-release.apk
• app-x86_64-release.apk
• Debug APK via https://appetize.io

Web build has been deployed to https://example-5dqy2g6ol-flutter-widget-from-html.vercel.app. Quick links:

• supported/tags.html
• Hello World
• Hello World (core)
• Wordpress

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (2b48b5d) 99.44% compared to head (b8b1d81) 99.44%.

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #1027   +/-   ##
=======================================
  Coverage   99.44%   99.44%           
=======================================
  Files          66       66           
  Lines        3986     3988    +2     
=======================================
+ Hits         3964     3966    +2     
  Misses         22       22           

Files	Coverage Δ
packages/core/lib/src/core_data.dart	100.00% <ø> (ø)
packages/core/lib/src/core_legacy.dart	100.00% <100.00%> (ø)
packages/core/lib/src/core_widget_factory.dart	100.00% <100.00%> (ø)
packages/core/lib/src/data/build_bits.dart	100.00% <ø> (ø)
packages/core/lib/src/data/html_style.dart	100.00% <100.00%> (ø)
...es/core/lib/src/internal/ops/style_background.dart	100.00% <100.00%> (ø)
...es/core/lib/src/internal/ops/style_text_align.dart	100.00% <100.00%> (ø)
...re/lib/src/internal/ops/style_text_decoration.dart	100.00% <100.00%> (ø)
packages/core/lib/src/internal/ops/tag_a.dart	100.00% <100.00%> (ø)
packages/core/lib/src/internal/ops/tag_li.dart	100.00% <100.00%> (ø)
... and 1 more

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