Migrate Apple native builds from Xcode projects to GN

[mattleibow]

Fixes #4168

Summary

Migrate the Apple native builds (libSkiaSharp + libHarfBuzzSharp for macOS, iOS, tvOS and Mac Catalyst) off the hand-maintained Xcode projects and onto the existing GN skiasharp_build targets — the same path Linux, Windows, WASM and Android already use.

Lands cleanly off main (independent of the in-flight C-API-move work) to give a simpler baseline and avoid conflicts. Requires the submodule half: mono/skia#256.

Changes

• Delete all 6 *.xcodeproj bundles (ios/tvos/macos × both libs) and scripts/infra/native/apple/xcode.cake.
• Rewrite native/{ios,tvos,macos}/build.cake to drive GN/ninja only.
• Add scripts/infra/native/apple/apple.cake (CombineFrameworks, StripSign, RunLipo, RunZip) for the post-GN lipo/strip/codesign/zip steps.
• macOS ships a plain fat .dylib (@rpath/lib<N>.dylib); iOS/tvOS/MacCatalyst frameworks are emitted directly by GN with link-time framework-relative install_name and a provenance-complete Info.plist; Cake only lipos the per-arch frameworks together and strips/codesigns last.
• Bump externals/skia to pull in the GN-emits-framework support (Emit Apple .framework from the skiasharp_build GN target skia#256).
• Document the new pure-GN flow in update-skia known-gotchas (Text measurement support #23).

Verification

Built from source for every Apple platform and checked against the released 3.119.0 baseline (per platform × both libs):

• symbol counts (887 sk_/gr_, 560 hb_)
• fat archs (x86_64 arm64)
• framework-relative install_name (Versions/A/ for Mac Catalyst)
• valid codesign
• sim slices: x86_64 → LC_VERSION_MIN_*, arm64 → LC_BUILD_VERSION
• Info.plist key set identical to the released NuGets (Mac Catalyst: UIDeviceFamily [2], LSMinimumSystemVersion 10.15)

Runtime tests: iOS simulator (iPhone 14 Pro) and Mac Catalyst both pass 5548 / 0.

Dependency

• Submodule: Emit Apple .framework from the skiasharp_build GN target skia#256 (base skiasharp). Merge that first, then this PR's submodule pointer is valid.

[github-actions]

📦 Try the packages from this PR

Warning

Do not run these scripts without first reviewing the code in this PR.

Step 1 — Download the packages

bash / macOS / Linux:

curl -fsSL https://raw.githubusercontent.com/mono/SkiaSharp/main/scripts/get-skiasharp-pr.sh | bash -s -- 4164

PowerShell / Windows:

iex "& { $(irm https://raw.githubusercontent.com/mono/SkiaSharp/main/scripts/get-skiasharp-pr.ps1) } 4164"

Step 2 — Add the local NuGet source

dotnet nuget add source ~/.skiasharp/hives/pr-4164/packages --name skiasharp-pr-4164

More options

Option	Description
--successful-only / -SuccessfulOnly	Only use successful builds
--force / -Force	Overwrite previously downloaded packages
--list / -List	List available artifacts without downloading
--build-id ID / -BuildId ID	Download from a specific build

Or download manually from Azure Pipelines — look for the nuget artifact on the build for this PR.

Remove the source when you're done:

dotnet nuget remove source skiasharp-pr-4164

[github-actions]

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