[Patterns] Syntax highlighters implementation

[itsjustkevin]

Cobbling together the list from past issues:

• https://github.com/dart-lang/dart-syntax-highlight/ (@DanTup)
  • Support modifiers + patterns dart-syntax-highlight#38
• https://github.com/highlightjs/highlight.js (@srawlins)
  • issue: [Request] support new Dart language keywords highlightjs/highlight.js#3725
  • PR: enh(dart) Add base, interface, sealed, and when keywords highlightjs/highlight.js#3726
• https://github.com/codemirror/CodeMirror/ (@domesticmouse)

[srawlins]

A note for tracking: These features are completed "out-of-band": they do not require changes to the Dart SDK or the Flutter repositories, so they can be landed after the Beta 3 deadline. I think it is still good to track them with the Beta 3 milestone for now.

[itsjustkevin]

Agree that this should be done before stable. From my perspective, this is still part of the minimum viable product. I would like to continue tracking this in beta 3, but will take a look again after we have filtered down the items in beta 3.

[vsmenon]

@domesticmouse - per checklist above - is there any work here you were planning on? And anything blocking?

[domesticmouse]

@domesticmouse - per checklist above - is there any work here you were planning on? And anything blocking?

I believe CodeMirror is in a good place. I added the new keywords in codemirror/codemirror5@6a70589 and codemirror/codemirror5@c17c5f0

[vsmenon]

Thanks - can we close this?

[vsmenon]

I'll close.