Fix deprecated Maven testing API compatibility

[goutamadwant]

Summary

• recognize the deprecated org.apache.maven.api.plugin.testing.Basedir annotation while preserving precedence for the replacement annotation
• restore the five-argument constructor on the deprecated ProducedArtifactStub compatibility class
• add regression coverage for the deprecated annotation flow and constructor source compatibility

This keeps the deprecated testing API functional for its remaining lifetime instead of allowing existing plugin tests to compile but silently use the wrong base directory.

Fixes #12678.

Verification

• mvn --batch-mode verify
• mvn --batch-mode -pl impl/maven-testing -am verify
• mvn --batch-mode -pl impl/maven-testing -am -rf :maven-testing -Dtest=ExpressionEvaluatorTest,ProducedArtifactStubTest -Dsurefire.failIfNoSpecifiedTests=false test

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[gnodet]

Correct, well-scoped fix for issue #12678. The findBasedirValue method follows the exact pattern already established by findInjectMojoAttrs and isRealSession for handling deprecated annotation fallback. The ProducedArtifactStub constructor restoration is also correct. Both changes have targeted regression tests.

Minor note (out of scope for this PR): The same missing-constructor issue exists in the deprecated ArtifactStub shim and in the deprecated SessionStub shim — these represent the same class of bug but are separate fixes.

This review was generated by an AI agent and may contain inaccuracies. Please verify all suggestions before applying.

Claude Code on behalf of gnodet