Create Dart breadcrumb provider

[danielway]

This introduces a breadcrumb provider for the Dart language, addressing WEB-33823 and flutter/flutter-intellij#3576.

This should generate crumbs for:

• Classes, methods, functions, getters/setters, mixins, enums, and non-local variables
• Unit tests and groups
• Nested constructors, with deep nesting in Flutter in mind

A class method:

Unit tests and groups.

Nested constructors.

This is building on the work of @greglittlefield-wf's branch and @jwren's earlier PR #739.

[alexander-doroshko]

Thank you for the pull request.

Please expect some delay with the review. We are going to try using the Outline data from the Analysis Server for breadcrumbs in Dart. Analysis Server knows Dart code better than the Dart plugin and it would be great to use its capabilities for all the features where possible.

The feature is on the roadmap, so I hope it will be fixed soon.

[bartekpacia]

Hi, sorry for posting messages likes this, but... any updates? Which Q can we expect this to land in?

[alexander-doroshko]

Unfortunately, I'm going to decline this PR because we'd like to use a different approach for the Dart breadcrumbs support. We'd like not to introduce new features based on the Dart plugin-specific parser (aka PSI, i.e. classes like DartComponent etc.), but use information from the Dart Analysis Server instead. The Analysis Server knows Dart code better than the Dart plugin and it would be great to use its capabilities for all the features where possible.

The feature is on the roadmap, but unfortunately, there's no specific ETA.