Add Maven compiler problem matcher for javac diagnostics

[brunoborges]

Description:

The javac problem matcher registered by setup-java only recognizes javac's native diagnostic format (File.java:12: warning: msg). That works for plain javac and for Gradle (which passes diagnostics through unchanged), but not for Maven. The maven-compiler-plugin reformats every diagnostic to [WARNING] /path/File.java:[12,5] msg, so the existing regex never matches and Maven builds produce zero GitHub annotations even though the warnings/errors appear in the log.

This adds a new maven-javac problem matcher owner to .github/java.json that recognizes the Maven format and captures severity, file, line, column, and message. A separate owner is used because multiple patterns under one owner are treated as a multiline sequence, not as alternatives. Both owners are registered by the same existing ##[add-matcher] call, so no source change is needed. Maven builds now annotate consistently with Gradle and plain javac.

Notes:

• The existing java and javac owners are unchanged, so current behavior is preserved.
• java.json is loaded at runtime by the runner and is not part of the webpack bundle, so dist/ does not need regeneration.
• GitHub matches the severity value case-insensitively, so capturing the uppercase WARNING/ERROR labels works.

Related issue:

Fixes: #1085

Check list:

• Ran npm run check locally (format, lint, build, test) and all checks pass.
• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[Copilot]

Pull request overview

Adds Maven-specific javac diagnostic matching to actions/setup-java’s existing Java problem matcher so Maven compiler warnings/errors produce GitHub annotations (consistent with plain javac and Gradle).

Changes:

• Adds a new problem matcher owner (maven-javac) that matches maven-compiler-plugin’s [WARNING]/[ERROR] /path/File.java:[line,col] message format.
• Keeps existing java and javac matcher owners unchanged to preserve current behavior.

Show a summary per file

File	Description
.github/java.json	Adds a maven-javac matcher pattern to recognize Maven compiler plugin diagnostics and enable annotations.

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