Add native Windows ARM64 (WoA) build support to mediapipe

[tsomanna]

PR Summary:
This PR enables native Windows ARM64 (WoA) support in MediaPipe using MSVC.

Changes:

1. Build and platform:

   • New windows_arm64 Bazel config and platform
   • Updated platform_mappings for windows arm64
   • .bazelrc configuration with ARM64‑specific and MSVC flags

2. Third party dependency changes:

   • ARM64 support/fixes for gflags, XNNPACK, cpuinfo, pthreadpool, pffft, ICU
   • Added opencv_windows_arm64 BUILD and repo for prebuilt OpenCV ARM64

3. Test fixes:

   • Guarded tests relying on pthreads or unsupported MSVC ARM64 behavior

4. Packaging:

   • setup.py auto‑enables --config=windows_arm64 on native WoA
   • GPU and ODML converter disabled on Windows ARM64

5. Error Fixing:
   Error: C2475: 'mediapipe::kGpuService': redefinition; 'constinit' specifier mismatch
   Fix: Added ABSL_CONST_INIT to kGpuService in mediapipe/gpu/gpu_service.cc to ensure the declaration and definition match, satisfying the MSVC compiler strictness.

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