[tests] organize/consolidate/de-duplicate shared or shareable analyzer/server/linter test logic

[pq]

There are at least a few tasks that could go towards improving test maintenance and authoring, leading to improved velocity, less technical debt and hopefully more fun (and better coverage) when writing tests.

De-Duplication. Analyzer, Linter and Server tests have a bit of duplication. Logic that's duplicated adds maintenance and confusion when once shared logic diverges.

• Move analyzer test utilities to analyzer_testing package #55660
• rationalize/unify test lint registration - c87b185

Unification. Besides duplication, we have many tests that test similar things but in subtly different ways. (Anecdotally, my recent language feature implementation tasks have been largely dominated by test authoring that in turn was largely dominated by answering questions of the "am I holding this right" kind.) Unification would speed up test-authoring and would have as a side-effect less test code to maintain.

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@dart-lang/analyzer-team: I'm taking a look at this and will update this item with concrete proposals and ideas. In the meantime, please feel free to chime in with thoughts/ideas!

[srawlins]

Close the existing issue, #55660, in favor of this one?

[pq]

Or maybe better still, treat this as a meta topic and link to that one. Thanks!