add enumsource exclude reinclude functionality again

[carstenartur]

What it does

Second work package from #2744 (first was #2907 — disable/enable test). Adds right-click context menu support in the JUnit test viewer to exclude specific enum values from @EnumSource parameterized tests and re-include them.

New infrastructure

• EnumSourceValidator — Reads/writes @EnumSource annotation state via AST bindings: checks EXCLUDE mode, extracts excluded names, removes exclusions, strips [N] display-name prefix to recover enum constant names
• ParameterizedTestMetadataExtractor — Lazily populates isParameterizedTest / parameterSourceType / parameterEnumType on TestCaseElement by parsing AST on demand; result is cached to avoid repeated parses
• TestAnnotationModifier.excludeEnumValue(IMethod, String) — AST rewrite that converts @EnumSource(Foo.class) → @EnumSource(value=Foo.class, mode=Mode.EXCLUDE, names={"X"}), or appends to an existing exclusion list

New actions

Action	Trigger	Effect
ExcludeParameterValueAction	Right-click TestCaseElement under @EnumSource	Adds value to names with mode=EXCLUDE; warns when ≤1 values remain
ReincludeAllEnumValuesAction	Submenu on TestSuiteElement	Removes mode + names attributes entirely; cleans up Mode import
ReincludeEnumValueAction	Submenu entry per excluded name	Removes one name; removes mode+names when list becomes empty

Model / UI changes

• TestCaseElement — Three new fields: fIsParameterizedTest, fParameterSourceType, fParameterEnumType
• TestSuiteElement — Added getSingleDynamicChild()
• TestViewer — Wires ExcludeParameterValueAction for case elements; addReincludeExcludedValuesSubmenu() builds the re-include submenu when isExcludeMode() is true
• TestSessionLabelProvider — Flat-layout label appends [@EnumSource(EnumType)] when metadata is populated

Tests

ExcludeParameterValueDisplayNameTest covers: initial exclude, append to existing exclusion list, remove-all, remove-single-value (including last-value-clears-mode), display-name stripping, and computeNamesAfterReinclude edge cases.

How to test

Author checklist

• I have thoroughly tested my changes
• The change is following the coding conventions
• I have signed the Eclipse Contributor Agreement (ECA)