Generate shared CSS property identity metadata

[danwalmsley]

Summary

• make the checked-in CSS metadata catalog the source for managed stable property IDs, managed CSSOM support, native CSSOM CSS/IDL name pairs, and the native effective-property table
• preserve all 105 managed storage IDs and the native compatibility aliases while replacing the handwritten 152-name V8 CSSStyleDeclaration list
• precompute native IDL names at generation time, avoiding runtime conversion allocations during V8 template setup
• expose the 14 logical effective properties that were previously missing from one or both CSSOM catalogs
• track the generator explicitly despite the repository-wide tools ignore rule
• add generated-output, stable-ID, managed regression, and browser-shaped WPT coverage

Validation

• metadata generator unit tests: 6/6; generated output check passes
• dotnet build WebScene.sln -c Release --no-restore: passes with 16 pre-existing nullable warnings, 0 errors
• dotnet test WebScene.sln -c Release --no-build --no-restore: 1,774 passed, 30 platform-dependent skipped, 0 failed
• Chrome 153 CSSOM contract: 5/5
• native current CSSParser CSSOM contract: 5/5
• native legacy parser CSSOM contract: 5/5
• current native CSS parser CTest: 1/1
• NativeWeb CSS service/shared-style/compiler CTests: 3/3
• current and legacy native engine libraries rebuild successfully against rebased main

An adjacent cssom- sweep passes every CSS-specific document. Its only failure is the unrelated existing document.cookie assertion in the combined DOM/CSSOM primitives contract, reproduced with fresh storage; no property-exposure assertion fails.

Advances #235 without touching the timing/containment work in #238 or stylesheet-finalization work in #297.