Add config for disable arrows in diff

[Mingpan]

This PR fixes:

• Can't revert change that deletes a single empty line in side-by-side diff editor #152165 - one can now revert single added empty line.
• New arrow to revert changes in diff editor interferes with setting breakpoints from diff editor #152115 - one can now disable the revert icons in diff editor from setting.

This PR adds a config setting for diff editor. The setting allows user to disable revert change icons in the glyph margin of a side-by-side diff editor.

CC @hediet

Some additional notes:

• I implemented this in a way that's similar to other existing settings in diffEditorWidget.ts, please let me know if some other pattern is preferred instead.
• Tooltips for glyph margin icons / decorations is not covered in this PR. A separate issue tracks it.

Please let me know if there's anything in the code that needs fixes / improvements. Thanks!

[hediet]

Thanks a lot for the PR!

[masterwishx]

i cant see arrow in diff for copy changes ...