Allow strong-typed metrics with 30+ tags

[adhikareeprayush]

Summary

• Remove the 30-tag limit (METGEN013) for strong-typed metrics in Microsoft.Gen.Metrics
• Strong-typed metrics like [Counter(typeof(SomeType))] can now have more than 30 tag names, same as [Counter("D1", ..., "D33")]
• Retire diagnostic METGEN013; the ID is left reserved so it is not reused

Fixes #7573

Test plan

• Parser tests accept strong-typed metrics with 33+ tags (histogram and gauge)
• Generated/runtime test records a 33-tag strong-typed counter
• Microsoft.Gen.Metrics.Unit.Tests pass
• Microsoft.Gen.Metrics.Generated.Tests pass on net8.0, net9.0, and net10.0

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR updates the Microsoft.Gen.Metrics source generator to allow strong-typed metrics (e.g., [Counter(typeof(MyDimensions))]) to use more than 30 tag names, matching the behavior already allowed when tag names are provided explicitly in the attribute. It also retires diagnostic METGEN013 (while keeping the ID reserved).

Changes:

• Removed the generator’s 30-tag strong-type limit check and retired the METGEN013 diagnostic descriptor/resources.
• Updated/added parser tests to validate strong-typed metrics with 33+ tags (including gauge/histogram scenarios).
• Added a generated/runtime test that emits and validates a 33-tag strong-typed counter end-to-end.

Reviewed changes

Copilot reviewed 7 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/Generators/Microsoft.Gen.Metrics/Unit/ParserTests.StrongTypes.cs	Updates strong-type parser test to validate >30 dimensions without diagnostics.
test/Generators/Microsoft.Gen.Metrics/Unit/ParserTests.Diagnostics.cs	Removes the old “too many dimensions” diagnostic test and replaces gauge test to ensure >30 tags succeeds.
test/Generators/Microsoft.Gen.Metrics/TestClasses/ManyTagsTestExtensions.cs	Adds test input types/extensions to generate and exercise a 33-tag strong-typed counter.
test/Generators/Microsoft.Gen.Metrics/Generated/MetricTests.cs	Adds end-to-end verification that a 33-tag strong-typed counter records expected tags/values.
src/Generators/Microsoft.Gen.Metrics/Resources.resx	Removes localized strings for the retired METGEN013 diagnostic.
src/Generators/Microsoft.Gen.Metrics/Resources.Designer.cs	Removes the generated resource accessors for the retired METGEN013 strings.
src/Generators/Microsoft.Gen.Metrics/Parser.cs	Removes the strong-type tag count enforcement that produced METGEN013.
src/Generators/Microsoft.Gen.Metrics/DiagDescriptors.cs	Removes the METGEN013 diagnostic descriptor definition.
docs/list-of-diagnostics.md	Removes METGEN013 from the published diagnostics list.

Files not reviewed (1)

• src/Generators/Microsoft.Gen.Metrics/Resources.Designer.cs: Generated file

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