Replace externals with Conan (#3735)

* Remove git submodules that will be loaded through conan

* Move custom Find modules to their own folder

* Use conan for downloading missing external dependencies

* CI: Change the yuzu source folder user to the user that the containers run on

* Attempt to remove dirty mingw build hack

* Install conan on the msvc build

* Only set release build type when using not using multi config generator

* Re-add qt bundled to workaround an issue with conan qt not downloading prebuilt binaries

* Add workaround for submodules that use legacy CMAKE variables

* Re-add USE_BUNDLED_QT on the msvc build bot

externals/find-modules/Findopus.cmake

@@ -0,0 +1,42 @@
+
+find_package(PkgConfig QUIET)
+pkg_check_modules(PC_opus QUIET opus)
+
+find_path(opus_INCLUDE_DIR
+  NAMES opus.h
+  PATHS ${PC_opus_INCLUDE_DIRS}
+  PATH_SUFFIXES opus
+)
+find_library(opus_LIBRARY
+  NAMES opus
+  PATHS ${PC_opus_LIBRARY_DIRS}
+)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(opus
+  FOUND_VAR opus_FOUND
+  REQUIRED_VARS
+    opus_LIBRARY
+    opus_INCLUDE_DIR
+  VERSION_VAR opus_VERSION
+)
+
+if(opus_FOUND)
+  set(Opus_LIBRARIES ${opus_LIBRARY})
+  set(Opus_INCLUDE_DIRS ${opus_INCLUDE_DIR})
+  set(Opus_DEFINITIONS ${PC_opus_CFLAGS_OTHER})
+endif()
+
+if(opus_FOUND AND NOT TARGET Opus::Opus)
+  add_library(Opus::Opus UNKNOWN IMPORTED)
+  set_target_properties(Opus::Opus PROPERTIES
+    IMPORTED_LOCATION "${opus_LIBRARY}"
+    INTERFACE_COMPILE_OPTIONS "${PC_opus_CFLAGS_OTHER}"
+    INTERFACE_INCLUDE_DIRECTORIES "${opus_INCLUDE_DIR}"
+  )
+endif()
+
+mark_as_advanced(
+    opus_INCLUDE_DIR
+    opus_LIBRARY
+)