Expand the CSC problem matcher to light up more errors on GitHub.

[StephenCleary]

Description:

This extends the csc problem matcher to support more flexible error message syntax, with tests. All examples have been seen in actual GHA runner output (these are anonymized real-world cases).

There are three changes to the regex:

• At the beginning of the line, whitespace and msbuild-style project number prefixes (e.g., 10>) are allowed. This is necessary for dotnet msbuild error parsing as well as dotnet build error parsing in some scenarios.
• Column numbers are now captured.
• Error codes no longer need to end in a number. This is necessary for dotnet format error parsing.

Related issue:

Replaces #691. Also see #583 which takes the alternative approach of adding an independent problem matcher for dotnet format (this PR includes dotnet format errors in the csc problem matcher).

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[Copilot]

Pull request overview

This PR expands the GitHub Actions CSC problem matcher regex so it recognizes a wider variety of real-world compiler/analyzer error formats (including dotnet msbuild prefixes and dotnet format-style codes), and updates tests to cover the new parsing behavior.

Changes:

• Updated .github/csc.json regex to allow leading whitespace and optional MSBuild project-number prefixes (e.g., 20>), capture column numbers, and allow non-numeric error codes.
• Extended Jest coverage with multiple real-world-inspired matcher examples (including dotnet format and MSBuild-prefixed output).
• Refactored the test to use test.each for clearer case-by-case validation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
__tests__/csc.test.ts	Adds multiple test cases validating the expanded matcher behavior and captured groups (including column).
.github/csc.json	Expands the matcher regex and updates capture-group mapping (adds column, shifts indices).

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[StephenCleary]

CC @baronfel

[baronfel]

LGTM from MSBuild team side!

[Frulfump]

Nice now we just have to wait for the maintainers of this repo and they are always super slow #701
One could clear the backlog of this repo in a week with AI but I think they are aiming for job security...