Track Xsemantics generated Java and stop Maven regeneration 🤖

[lwrage]

Fixes #3258

Maven currently deletes ALISA's generated Xsemantics Java during clean and regenerates it during source generation. Track the six existing generated interpreter, type-system, and validator sources so Maven can compile them directly.

Remove the Xsemantics generation configuration, generator dependencies, and clean filesets from the main and experimental GE parent POMs, along with the ALISA and BA plugin declarations that inherit that configuration. Keep ._trace files ignored and update the comment describing the inherited clean fileset.

Validation

Ran from a clean, isolated checkout of the PR commit:

mvn -o -T5 -s releng/osate.releng/settings.xml -Plocal \
  -Dtycho.localArtifacts=ignore -Dpr.build=true -Dsign=false \
  -Dspotbugs=false -Dcodecoverage=false -Djavadoc=false \
  -DfailIfNoTests=false clean install

• All 143 reactor projects succeeded.
• Surefire reports contain 1,690 tests across 15 bundles, with zero failures, errors, or skips.
• This includes all 30 existing AssureTests, which exercise parsing, validation, and assurance evaluation using the models/SimpleControlSystem fixtures.
• All six generated Java files remained byte-for-byte identical to the committed sources. No Xsemantics generation ran, and the clean checkout built without trace files.
• Configuration changes pass the whitespace check. Existing generated whitespace is preserved.

Dependencies and risk

Targets master with no dependency on an unmerged PR. The generated Java is unchanged; the maintenance requirement is to regenerate it explicitly in Eclipse and commit the output whenever the .xsemantics definitions change.