[browser] Append uniqueness to webcil temp path & move instead of copy

[maraf]

• Append unique guid for every execution of ConvertDllsToWebcil to the temp files path
• Use "move" filesystem operation instead of "copy" if temp file is different than the final one

Contributes to dotnet/aspnetcore#61987

[Copilot]

Pull Request Overview

This PR improves the file handling in the WebCil conversion process for WebAssembly by implementing two key optimizations: using unique temporary directories to avoid conflicts and replacing file copy operations with more efficient move operations when possible.

• Generates unique temporary directory paths using GUIDs to prevent conflicts during concurrent builds
• Replaces copy operations with move operations for better performance when temporary and final files are different
• Adds cleanup of temporary directories after processing

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
ConvertDllsToWebCil.cs	Updates temp directory creation with GUID uniqueness, adds directory cleanup, and switches from copy to move operations
Utils.cs	Adds new MoveIfDifferent method with cross-framework compatibility for file move operations

Comments suppressed due to low confidence (1)

[maraf]

/ba-g Linux failure in PInvokeTableGeneratorTests.UnmanagedStructsAreConsideredBlittableFromDifferentAssembly has a Windows variant passing at https://helix.dot.net/api/jobs/adffa14d-7513-4e3b-b09e-82bb353cd520/workitems/Workloads-ST-Wasm.Build.Tests.PInvokeTableGeneratorTests?api-version=2019-06-17

[maraf]

/backport to release/10.0-staging

[github-actions]

Started backporting to release/10.0-staging: https://github.com/dotnet/runtime/actions/runs/17375531804

[github-actions]

@maraf an error occurred while backporting to "release/10.0-staging", please check the run log for details!

Error: The specified backport target branch "release/10.0-staging" wasn't found in the repo.

[maraf]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/17396752005