☂️ Deprecate Intel on macOS #188328

See Design Doc: https://flutter.dev/go/macos-intel-deprecation

Stage 0: Announce planned reduction of support

• Print a warning when building on a Intel machine that support will be unavailable in a future release #188330
• Print a warning when building a macOS app that supports both Intel and ARM and guide to enable feature flag #188333

Stage 1: Remove Rosetta requirement

• ☂️ [macOS] Support building engine on Apple Silicon without Rosetta #103386
• Investigate and eliminate Rosetta requirement from gen_snapshot #188386
• Investigate and eliminate Rosetta requirement on devicelab bots #193716

Stage 2: Reduce support by removing Intel bots from CI

• Remove Intel test builders that already run on ARM #189295
• Migrate flutter/flutter CI x86 builds to ARM #189144
• When building a macOS app with Xcode 27+, default to build ARM-only #189136
• Remove tool_host_cross_arch_tests test shard #189302
• Running Mac framework_tests* on arm64 Macs flakes with "Skia Gold received an unapproved image in post-submit" #119880
• Migrate flutter/packages CI macOS x86 builds to ARM #190531

Stage 3: Stop support for development on Intel-machines

• Flutter CLI error/warns if attempting to build on macOS Intel machine #194095
• Remove x86_64 architecture from development binaries for macOS #194097
• Remove x86_64 architecture from Flutter.xcframework for iOS simulator #194094
• Remove x86_64 architecture from gen_snapshot for iOS on macOS #194093
• Remove x86_64 architecture from gen_snapshot for Android on macOS #194092
• Remove x86_64 architecture from ios-usb-dependencies binaries #194098

Stage 4: Stop support for building universal macOS apps

• Flutter CLI errors if attempting to build an Intel macOS app
• FlutterMacOS.xcframework should be converted to ARM-only (e.g. macos-arm64_x86_64 -> macos-arm64)
• Intel specific DEPS can be removed (1, 2, 3, 4)
• Intel specific toolchains can be removed (1, 2)
• Remove Intel specific skia things (1, 2, 3)
• Optional: Change artifact cache path from darwin-x64 to darwin-arm64 for Android and macOS