Unify ANGLE dependency into Skia DEPS file

[mattleibow]

Move ANGLE from a standalone git clone in winui-angle/build.cake into the Skia DEPS file using the deps_os["win"] conditional section. This means git-sync-deps handles ANGLE checkout alongside all other dependencies, but only on Windows where it's needed for WinUI builds.

Companion PR: mono/skia#183 — adds the deps_os["win"] entry to DEPS

What changed

File	Change
externals/skia	Points to skia commit with deps_os["win"] ANGLE entry
scripts/cake/native-shared.cake	Passes OS arg to git-sync-deps; adds SyncAngle() for submodule init + setup
native/winui-angle/build.cake	Removes clone/setup logic from sync-ANGLE; updates ANGLE_PATH to new location; keeps WinAppSDK setup + build tasks
scripts/cake/externals.cake	Updates clean path to new ANGLE location
scripts/VERSIONS.txt	Notes that DEPS is the source of truth for ANGLE pin

How it works

1. git-sync-deps in the DEPS file now has a deps_os section:

   deps_os = {
       "win": {
           "third_party/externals/angle2": "https://github.com/google/angle.git@ea1cea...",
       },
   }

2. The cake git-sync-deps task passes "win" / "mac" / "unix" as a CLI arg so platform-conditional deps are synced
3. After sync, SyncAngle() inits only the 7 required submodules and runs post-checkout setup (patches, gclient_args, LASTCHANGE, rc.exe, LLVM)
4. sync-ANGLE in the ANGLE build file now only handles WinAppSDK generation — all other setup moved to shared sync

Benefits

• Single DEPS file is the source of truth for all native dependencies including ANGLE
• Single sync task (git-sync-deps) handles everything
• Zero cost on non-Windows CI — deps_os["win"] entries are only fetched when OS arg is "win"
• ANGLE version pin is visible alongside all other dependency pins

[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 -- 3701

PowerShell / Windows:

iex "& { $(irm https://raw.githubusercontent.com/mono/SkiaSharp/main/scripts/get-skiasharp-pr.ps1) } 3701"

Step 2 — Add the local NuGet source

dotnet nuget add source ~/.skiasharp/hives/pr-3701/packages --name skiasharp-pr-3701

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-3701