feat: macOS ICU build

[ramezgerges]

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• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
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[Copilot]

Pull Request Overview

This PR adds macOS support to the Uno ICU library by creating a new uno.icu-macos NuGet package and updating the build process to compile ICU libraries for macOS platforms.

• Adds build jobs for creating universal macOS ICU binaries (x86_64 and arm64)
• Creates new uno.icu-macos NuGet package specification for macOS ICU libraries
• Restructures the existing build process to support multiple target platforms

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
.github/workflows/main.yml	Adds macOS build jobs and restructures artifact handling to support both WASM and macOS targets
nuget/uno.icu-macos/uno.icu-macos.nuspec	Creates NuGet package specification for macOS ICU libraries
nuget/uno.icu-wasm/buildTransitive/Uno.icu-wasm.targets	Adds MSBuild targets for WASM native file references
nuget/uno.icu-wasm/build/Uno.icu-wasm.targets	Removes WebAssembly-specific condition from embedded resource inclusion
nuget/buildTransitive/Uno.icu-wasm.targets	Removes old build targets file (moved to package-specific location)

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[jeromelaban]

aside from copilot's comments, looks good

[spouliot]

The changes LGTM but I lack context. Is this only for web assembly on macOS ?

[ramezgerges]

@spouliot No, it's for the desktop target. I'm working on a new text handling implementation that is Unicode-aware, which uses ICU for stuff like line segmentation and BiDi, so we need a package that provides the ICU binaries.