DolphinQt/CMakeLists: Leverage windeployqt for determining libraries and plugins to copy

We were doing quite a bit of unnecessary work within CMake to handle and
make sure the necessary libraries were copied over. That approach has
several downsides:

1. It's not possible to handle multi-configuration generators (like
   Visual Studio) in an easy manner. The existing script would fail to
   copy over the necessary libraries if one configuration was built, and
   then another one was built.

2. If you have Qt already installed (properly) by the official binary,
   the existing script would copy *all* dlls even if they weren't
   necessary. This is pretty bad, since it can waste quite a bit of
   space.

Instead, we can just delegate off to the official deployment application
bundled with Qt's libraries that determines what the necessary libraries
are and copies them over as necessary. This also means we can properly
support both release and debug binaries in the same directory, like how
the old handcrafted Visual Studio project files allowed.

Source/Core/DolphinQt/CMakeLists.txt

@@ -296,47 +296,37 @@ if(WIN32)
 
   # Copy qt.conf
   add_custom_command(TARGET dolphin-emu POST_BUILD
-   COMMAND ${CMAKE_COMMAND} -E copy_if_different "${CMAKE_CURRENT_SOURCE_DIR}/qt.conf.win" "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/qt.conf"
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different "${CMAKE_CURRENT_SOURCE_DIR}/qt.conf.win" "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/qt.conf"
   )
 
-  # Create QtPlugins directory
+  # Delegate to Qt's official deployment binary on Windows to copy over the necessary Qt-specific libraries, etc.
+  get_target_property(MOC_EXECUTABLE_LOCATION Qt5::moc IMPORTED_LOCATION)
+  get_filename_component(QT_BINARY_DIRECTORY "${MOC_EXECUTABLE_LOCATION}" DIRECTORY)
+  find_program(WINDEPLOYQT_EXE windeployqt HINTS "${QT_BINARY_DIRECTORY}")
+
+  # Note: We set the PATH for the duration of this command so that the
+  #       deployment application is able to locate the Qt libraries to copy.
+  #       if the necessary paths aren't already set beforehand.
+  #
+  #       For example, consider a hypothetical emulation project named Orca.
+  #       Orca supplies its own version of Qt instead of having developers actually
+  #       install the officially supported Qt libraries -- a method that would make
+  #       wrangling around with Qt through CMake much nicer and lessen the external
+  #       library maintenance burden of the project, but alas.
+  #
+  #       In this case, as Qt is not installed through the official binary, this also
+  #       means proper path variables will not be set up, thus the need to ensure they're
+  #       always set up.
+  #
   add_custom_command(TARGET dolphin-emu POST_BUILD
-    COMMAND ${CMAKE_COMMAND} -E make_directory "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/QtPlugins"
+    COMMAND "${CMAKE_COMMAND}" -E env PATH="${QT_BINARY_DIRECTORY}"
+            "${WINDEPLOYQT_EXE}" --libdir="${CMAKE_RUNTIME_OUTPUT_DIRECTORY}"
+                                 --plugindir="${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/QtPlugins"
+                                 $<IF:$<CONFIG:Debug>,--debug,--release>
+                                 --no-translations
+                                 --no-compiler-runtime
+                                 "$<TARGET_FILE:dolphin-emu>"
   )
-
-  # Copy plugins
-  set (Qt5_PLUGINS_DIR "${Qt5_DIR}/../../../plugins")
-  file(GLOB_RECURSE plugins RELATIVE "${Qt5_PLUGINS_DIR}" "${Qt5_PLUGINS_DIR}/*.dll")
-
-  if (CMAKE_BUILD_TYPE STREQUAL "Debug")
-    list(FILTER plugins INCLUDE REGEX ".*d.dll")
-  else()
-    list(FILTER plugins EXCLUDE REGEX ".*d.dll")
-  endif()
-
-  foreach(plugin ${plugins})
-    add_custom_command(TARGET dolphin-emu POST_BUILD
-      COMMAND ${CMAKE_COMMAND} -E copy_if_different "${Qt5_PLUGINS_DIR}/${plugin}" "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/QtPlugins/${plugin}"
-    )
-  endforeach()
-
-  # Copy DLLs
-  set (Qt5_DLL_DIR "${Qt5_DIR}/../../../bin")
-
-  file(GLOB_RECURSE dlls RELATIVE "${Qt5_DLL_DIR}" "${Qt5_DLL_DIR}/*.dll")
-
-  if (CMAKE_BUILD_TYPE STREQUAL "Debug")
-    list(FILTER dlls INCLUDE REGEX ".*d.dll")
-  else()
-    list(FILTER dlls EXCLUDE REGEX ".*d.dll")
-  endif()
-
-  foreach(dll ${dlls})
-   add_custom_command(TARGET dolphin-emu POST_BUILD
-    COMMAND ${CMAKE_COMMAND} -E copy_if_different "${Qt5_DLL_DIR}/${dll}" "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}"
-   )
-  endforeach()
-
 endif()
 
 # Handle localization