Move AppKit (macOS) backend to winit-appkit (#4248)

.github/CODEOWNERS

@@ -2,9 +2,8 @@
 /winit-android                      @MarijnS95
 
 # Apple (AppKit + UIKit)
+/winit-appkit                       @madsmtm
 /winit-uikit                        @madsmtm
-/src/platform/macos.rs              @madsmtm
-/src/platform_impl/apple            @madsmtm
 /winit-common/src/core_foundation   @madsmtm
 /winit-common/src/event_handler.rs  @madsmtm
 

.github/workflows/ci.yml

@@ -197,6 +197,10 @@ jobs:
       if: contains(matrix.platform.target, 'linux-gnu')
       run: cargo $CMD test -p winit-common --features xkb,x11,wayland --no-run
 
+    - name: Test winit AppKit
+      if: contains(matrix.platform.target, 'macos')
+      run: cargo $CMD test -p winit-appkit --target=${{ matrix.platform.target }}
+
     - name: Test winit Orbital
       if: contains(matrix.platform.target, 'redox')
       run: cargo test -p winit-orbital