IDE tooling (analysis server) implementation for enhanced enums

[devoncarew]

This is the analysis server work for the enhanced enums feature.

For addition information, see

• main tracking issue (Implement enhanced enums #47849)
• specification

The following is a list of the individual features that need to be considered.

• Quick Assists
• Closing Labels
• Code Completion (scheglov)
• documentSymbol
• Quick Fixes (support for new features in existing fixes)
• Quick Fixes (new fixes)
• Flutter Outline (scheglov)
• Code Folding
• Hovers (scheglov)
• Implemented Markers (scheglov)
• Navigation (scheglov)
• Occurrences (scheglov)
• Organize Imports (brianwilkerson, NA)
• Outline (scheglov)
• Overrides Markers (scheglov)
• Refactorings (scheglov)
• Search - Find References (scheglov)
• Search - Member Declarations (scheglov)
• Search - Member References (scheglov)
• Search - Top-level Declarations (scheglov, NA)
• selectionRange
• Semantic Highlights (scheglov)
• signatureHelp
• Sort Members (scheglov)
• Type Hierarchy (scheglov)

[stereotype441]

Note: in particular, code completion will have to be modified so that:

• In an enum declaration, after the name of an enum constant, optional type arguments, and then a ., completion suggests the names of the enum's constructors
• In an enum declaration, after a ;, completion suggests everything that it would suggest inside a class declaration

[jacob314]

Fyi @pq for a prefer enums lint and quick fix that rewrites code that now could be an enum to enum.

[pq]

See also: #58624.

[itsjustkevin]

@bwilkerson is this feature work complete?

[bwilkerson]

Yes. If there is any further work that needs to be done I'd consider it a bug and I'd want a separate issue for it. In general, I think it's reasonable to close issues like this one after a feature has shipped. We probably need to be better about keeping these issues up-to-date, because they're really only useful if they help us understand what work might be gating a release, but once the feature has shipped I don't think they have any ongoing value.