Removing Nunit from utils

[psfinaki]

Related: #13654

TL;DR: We are nearly done!

• This removes Nunit from test frameworks
• Cleans things up
• Enables 32 valid ComponentTests that were silently not being executed

Please see my comments everywhere, this is close to the equivalent code, with minor simplifications and fixes.

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Note this increases the number of tests executed in the CI. The execution time is not affected.

Main:

This branch:

This is due to:

• 5 new tests in the FSharpSuite. Those are old-new AsyncTests and they are skipped anyway for now. See comment.
• 35 new tests in the ComponentTests.TypeChecks. Of those:
  • 2 CompilationFromCmdlineArgsTests and 1 TypedTreeGraphTests - those were explicit + failing, now skipped
  • 1 DependencyResolutionTests - this is legit and passing, wasn't being executed as [<Theory>] was forgotten there
  • 8 FileContentMappingTests, 1 GraphProcessingTests, 4 QueryTrieTests, 18 TrieMappingTests - those are legit and passing, weren't being executed because weren't rewritten to Xunit (so trying executing non-existing Nunit adapter)

[github-actions]

✅ No release notes required