Keep cursor position attached if exiting exploration after code edits

[rlisahuang]

If the cursor has been focused in the exploration panel before the user exits exploration (i.e., user exits after clicking around in the exploration panel), then the edited text would be highlighted, which is fine.

However, if the cursor has been focused inside the editor before exiting exploration (i.e., user exits after editing the code), then the cursor position would stick to its original line and column, but no longer attached to the same character (because that character might have moved!)

The workaround should be simple. Given the original cursor position (lineNumber, col), we need to refocus the selection on (lineNumber-1, col), because the code would be moved upward by one line due to the removal of one completion comment above.