Resolve classified POM artifacts from the reactor in Maven 3.x

[wilx]

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Description

Maven 3's ReactorReader returns the reactor project's build POM for every artifact request whose extension is pom, before considering the classifier. Consequently, resolving an attached classified POM from the reactor returns pom.xml instead of the attached artifact.

This change limits the build-POM shortcut to unclassified POM requests. Classified POMs proceed through the existing artifact-matching path, which selects the attached artifact by extension and classifier. A focused unit test reproduces the incorrect path before the fix and verifies the attached POM afterward.

This is the Maven 3.10.x counterpart to #12658.

Fixes apache/maven-dependency-plugin#1024

Tests

• Regression test before the fix: expected custom.pom, but ReactorReader returned pom.xml.
• Full root mvn verify: all 16 modules passed with RAT, Checkstyle, Spotless, Animal Sniffer, and unit tests enabled.
• maven-core: 367 tests, 0 failures, 0 errors, 1 skipped.
• Complete unfiltered Maven 3.10.x Core IT suite with run-its,embedded: all 78 modules passed; 867 tests, 0 failures, 0 errors, 39 skipped.

[gnodet]

Clean backport of the 4.x ReactorReader fix (PR #12658) to 3.x. The one-line production change is identical in logic, correctly adapted for the 3.x find() method signature.

The null-or-empty classifier guard is appropriately defensive, and the new unit test properly verifies the fix by exercising the full resolution path through findMatchingArtifact.

Note: the 4.x PR includes integration test resources under its/core-it-suite, but their absence here is expected since Maven 3.x core integration tests live in a separate repository (apache/maven-integration-testing). The unit test provides equivalent regression coverage.

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

Claude Code on behalf of gnodet