[Dot Shorthands] IntelliJ support

[kallentu]

This issue tracks the work needed for IntelliJ support for dot shorthands.
Spec: https://github.com/dart-lang/language/blob/main/working/3616%20-%20enum%20value%20shorthand/proposal-simple-lrhn.md

IntelliJ Issue:
https://youtrack.jetbrains.com/issue/IDEA-370100/New-Dart-language-feature-Dot-Shorthands

[kallentu]

YouTrack issue filed: https://youtrack.jetbrains.com/issue/IDEA-370100/New-Dart-language-feature-Dot-Shorthands

[bwilkerson]

This will minimally require an update to the IntelliJ parser, unless we decide to remove the parser before we want to ship this feature.

[kallentu]

Feature marked as fixed on the YouTrack issue. I'll close this now.