Make WebGPU browser tests portable across desktop platforms

[sureshchouksey8]

This moves the WebGPU browser-test portability fix to the currently maintained Effekseer LLGI fork. The same branch was originally opened against altseed/LLGI, but that PR was closed because that repository is not being updated.

Changes:

• find Chrome/Edge on macOS and Linux in addition to Windows
• avoid forcing Windows-only --use-angle=d3d11 outside Windows
• use ANGLE Metal on macOS
• document macOS CHROME_PATH usage for the WebGPU browser test

Verification completed locally:

• native LLGI target builds
• Emscripten WebGPU browser LLGI_Test target builds
• full real-Chrome WebGPU browser suite completes with LLGI_TEST_PASS completed
• downstream Effekseer WebGPU browser CTest passes against this PR head: 100% tests passed, 0 tests failed out of 1
• additional local Three.js-facing browser proof passes: actual Three.js creates a THREE.PerspectiveCamera; its matrices are passed into Effekseer WebGPU rendering; the effect output is validated by changed pixels and ends with EFFEKSEER_TEST_PASS completed

Related bounty/context issue: effekseer/EffekseerForWebGL#113

[sureshchouksey8]

I rebuilt this PR branch onto effekseer/LLGI:master so it is now a minimal one-commit / two-file PR instead of carrying stale WebGPU development commits from the older upstream.

Current PR head: 223e389
Current diff: only:

• src_test/browser/run_webgpu_browser_test.mjs
• docs/WebGPU_Browser_Test.md

I also revalidated downstream from Effekseer with nested Dev/Cpp/3rdParty/LLGI checked out to this exact PR head. Result:

ctest --test-dir build_effekseer_webgpu_browser -R Effekseer_WebGPU_Browser --output-on-failure

Passed in Chrome/WebGPU: 100% tests passed, 0 tests failed out of 1 (8.70 sec).