Validate repair event initiator types 🤖

[lwrage]

Fixes #2807.

Repair-event when clauses currently accept invalid initiators, while recover events report each invalid initiator twice. Both Xtext checks were registered for RecoverEvent. Register the repair check for RepairEvent and share the existing initiator type validation, retaining ports, internal events, and mode transitions as accepted types.

The first commit adds Issue2807Test and external AADL fixtures; the second fixes the validator. The regression verifies rejection of mode and subcomponent references, exactly one diagnostic per invalid initiator, and acceptance of valid initiators and absent when clauses. Before the fix, two tests failed for the reported behavior and the valid-model test passed.

Validation

Focused regression: 3 tests passed. Full EMV2 bundle: 296 tests passed. Both used:

mvn -o -T5 -s releng/osate.releng/settings.xml -Plocal \
  -pl :org.osate.xtext.aadl2.errormodel,:org.osate.aadl2.errormodel.tests,:org.osate.xtext.aadl2.errormodel.feature \
  -Dtycho.localArtifacts=default -Dpr.build=true -Dsign=false \
  -Dspotbugs=false -Dcodecoverage=false -Djavadoc=false \
  -Dtest=Issue2807Test -DfailIfNoTests=false clean verify

For the full EMV2 bundle run, omitted -Dtest and -DfailIfNoTests.

Clean root reactor: all 143 projects succeeded; Surefire reports contain 1,671 tests with no failures, errors, or skips.

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

git diff --check passed and the worktree is clean.

Dependencies and risk

No dependencies on unmerged PRs; targets master. The change is limited to event-initiator validation. Existing models with invalid repair-event initiators will now receive the intended errors.