Move Windows backend to winit-win32

.github/CODEOWNERS

@@ -21,9 +21,8 @@
 /src/platform/web.rs                @daxpedda
 /src/platform_impl/web              @daxpedda
 
-# Windows
-/src/platform/windows.rs            @notgull
-/src/platform_impl/windows          @notgull
+# Windows (Win32)
+/winit-win32                        @notgull
 
 # Orbital (Redox OS)
 /winit-orbital                      @jackpot51

.github/workflows/ci.yml

@@ -190,6 +190,10 @@ jobs:
       if: contains(matrix.platform.target, 'redox')
       run: cargo test -p winit-orbital
 
+    - name: Test winit Win32
+      if: contains(matrix.platform.target, 'windows')
+      run: cargo $CMD test -p winit-win32 --target=${{ matrix.platform.target }}
+
     # Test only on Linux x86_64, so we avoid spending unnecessary CI hours.
     - name: Test dpi crate
       if: >