Include workspace property sets in the property filter dialog 🤖

[lwrage]

Fixes #3234

Confirming the property-set filter dialog previously hid workspace property sets because the dialog only offered contributed sets. The dialog now reads workspace property sets from the Xtext index and makes them individually selectable under Workspace Property Sets, immediately after Predeclared Property Sets. The predeclared group label no longer contains underscores.

Issue3234Test replaces the previous characterization with a separate, validated AADL model project. It reproduces workspace properties disappearing after Select All, then verifies the fix, group ordering, an unimported workspace set, individual and group checkboxes, reopening, and cancellation. The branch contains the regression commit followed by the production fix.

Validation

The regression failed before the fix with both workspace sets missing from the view and the old underscored group label. After the fix, both regression tests passed:

mvn -o -s releng/osate.releng/settings.xml -Plocal,with-ui-tests \
  -pl :org.osate.xtext.aadl2.ui,:org.osate.core.feature,:org.osate.ui.tests \
  -Dtycho.localArtifacts=default -Dpr.build=true -Dsign=false \
  -Dspotbugs=false -Dcodecoverage=false -Djavadoc=false \
  -Dtest=Issue3234Test -DfailIfNoTests=false clean install

The clean root reactor passed all 144 modules and 1,690 tests, including 53 UI tests, with zero failures, errors, or skips:

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

Scope and dependencies

Targets master with no dependencies on unmerged PRs. Risk is limited to property-view filter selection and presentation; the change uses the existing URI-based filter and checkbox behavior, and workspace discovery relies on the Xtext index.