[MDEP-870] Overwrite copied artifact POMs

[wilx]

Summary

When dependency:copy-dependencies copies an artifact, overwrite its associated POM as well. This prevents version-stripped output from containing a JAR from one version and a pre-existing POM from another version.

Artifacts skipped by the configured overwrite policy retain the existing MDEP-164 behavior: their POM is copied only when it is missing.

Root cause

Copied and skipped artifacts shared the same copyPoms path, which unconditionally ignored an existing destination POM. As a result, an artifact selected for replacement could overwrite the versionless JAR while leaving its old versionless POM untouched.

Fixes #1370

Verification

• The new regression test failed before the production change with expected: <new pom> but was: <old pom>.
• Maven 3: mvn verify — 412 tests, 0 failures/errors, 1 skipped.
• Maven 4 with JDK 21: mvn verify — 412 tests, 0 failures/errors, 1 skipped.
• Focused Invoker build: mvn -DskipTests -Prun-its -Dinvoker.test=copy-dependencies verify — 1 passed.
• Exact Commons Lang 3.12.0 to 3.14.0 reproducer: the resulting versionless JAR and POM checksums both match 3.14.0.

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[wilx]

Suppressed: org.eclipse.aether.transfer.ArtifactTransferException: Could not transfer artifact org.ow2.asm:asm-util:pom:9.9 from/to central (https://repo.maven.apache.org/maven2): HTTP connect timed out

Some sort of infrastructure issue.