Rewrite host GPU abstraction

- Don't have to repeat the same thing for 4 renderers.
 - Add native Metal renderer.

src/duckstation-qt/CMakeLists.txt

@@ -198,7 +198,7 @@ if(WIN32)
   )
 endif()
 
-if(APPLE)
+if(APPLE AND NOT CMAKE_GENERATOR MATCHES "Xcode")
   set(BUNDLE_PATH ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/DuckStation.app)
 
   # Ask for an application bundle.