Add Eclipse release-matrix compatibility CI with parameterized Tycho target platform resolution

[Copilot]

This PR introduces an Eclipse-version compatibility check that builds the plugin against release targets from 2024-06 through 2026-03 without source edits per target. It parameterizes Tycho target selection and EE-constraint behavior so one codebase can be validated across older and newer Eclipse trains.

• Target platform matrix support

  • Added targets/ with 8 release-specific target files:
    • 2024-06, 2024-09, 2024-12, 2025-03, 2025-06, 2025-09, 2025-12, 2026-03
  • Each target keeps the same IU set as current baseline, only varying the release repository URL.

• Baseline target indirection

  • Updated target-platform.target to delegate to targets/2024-06.target via nested target reference.
  • Keeps baseline in one place while enabling matrix overrides.

• Maven/Tycho parameterization

  • Added root pom.xml properties:
    • target.platform.file (default: target-platform.target)
    • target.resolve.with.ee.constraints (default: true)
  • Wired into target-platform-configuration:
    • dynamic target file path
    • configurable resolveWithExecutionEnvironmentConstraints

• New CI workflow

  • Added .github/workflows/compatibility.yml:
    • Windows matrix build for the 8 Eclipse targets
    • Maven invocation with quoted -D... args (PowerShell-safe)
    • Per-target EE constraints:
      • true for 2024-*
      • false for 2025-03+ (to allow resolving JavaSE-21 IUs during compatibility checks)

run: mvn -B clean verify -ntp \
  "-Dtarget.platform.file=targets/${{ matrix.target }}.target" \
  "-Dtarget.resolve.with.ee.constraints=${{ startsWith(matrix.target, '2024-') && 'true' || 'false' }}"