Add native C++ coverage via OpenCppCoverage

[jasonleenaylor]

test.ps1 -Coverage now also collects native C++ coverage: Invoke-CppTest.ps1 gains a -Coverage switch that runs testGenericLib.exe and TestViews.exe under OpenCppCoverage (debugger-based, needs only the build's PDBs, never rewrites binaries in the shared Output/<Configuration> folder) and exports Output/<Configuration>/TestResults/native.<exe>.cobertura.xml. CI uploads the files under Codecov flag native, separate from managed.

Specifics:

• Cobertura paths are rewritten repo-relative so Codecov matches files on any checkout path (no fixes: needed).
• Without OpenCppCoverage installed (choco install opencppcoverage, or env OpenCppCoveragePath for a portable copy), native tests run bare with a [WARN]; CI then fails at the native upload step (fail_ci_if_error), never at the test step.
• Invoke-CppTest's post-summary grace kill is disabled under coverage — the export is written after the Unit++ summary prints and a kill there would truncate it; covered runs rely on the overall timeout, which now also stops the child exe.
• Shared plumbing consolidated into FwBuildHelpers.psm1: Set-TestAssertDialogEnvironment, Disable-CrashDialog, Get-UnitppSummary, Find-OpenCppCoverage, Convert-CoberturaPathsToRepoRelative.
• New composite action .github/actions/codecov-upload owns the Codecov attempt/retry/verify sequence and the pinned action SHA; both the managed and native uploads use it.
• CI installs OpenCppCoverage 0.9.9.0 (pinned) before the test step; codecov.yml ignores the native Unit++ test sources (Src/Generic/Test, Src/views/Test).

Measured: identical test results under coverage (testGenericLib [31-0-0], TestViews [301-0-0], exit 0); ~4x native wall time (TestViews ~5s -> ~20s); ~51% native line coverage across Views.dll, DebugProcs.dll, and the statically linked Generic sources; ReportGenerator 5.3.11 parses the files alone and merged with the managed report. All CI checks pass, including the native Codecov upload.

🤖 Generated with Claude Code

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This change is 

[github-actions]

NUnit Tests

    1 files  ±0      1 suites  ±0   11m 38s ⏱️ +6s
5 761 tests ±0  5 680 ✅ ±0  81 💤 ±0  0 ❌ ±0 
5 770 runs  ±0  5 689 ✅ ±0  81 💤 ±0  0 ❌ ±0 

Results for commit 6bd6f61. ± Comparison against base commit 64bba89.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.02%. Comparing base (8dd2468) to head (6bd6f61).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1049      +/-   ##
==========================================
+ Coverage   36.43%   38.02%   +1.58%     
==========================================
  Files        1354     1500     +146     
  Lines      295676   349932   +54256     
  Branches    40223    40228       +5     
==========================================
+ Hits       107742   133047   +25305     
- Misses     158661   187606   +28945     
- Partials    29273    29279       +6     

see 151 files with indirect coverage changes

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