docs: document deprecation rationale for getPomFile/setPomFile

[anukalp2804]

Fixes #11674

Documents the deprecation rationale and recommended replacement for the model API methods getPomFile() and setPomFile(File).

This change is documentation-only and does not affect runtime behavior.

Build: mvn -DskipTests -pl api/maven-api-model -am verify

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[cstamas]

This is again wrong, version 4.0.0 of Maven was not even released.

[anukalp2804]

Thanks — you’re right. I’ve replaced the JavaDoc link with plain text in the .mdo file and kept the deprecation version-agnostic.

[elharo]

This is pulling in changes from other PRs. remove from this PR

[anukalp2804]

Thanks for catching that — I’ve removed the unrelated Language.java changes so this PR now only contains the maven.mdo updates.