InputCommon: Update to use SDL3 and bump the SDL submodule in Externals to release-3.2.16.

Source/Core/InputCommon/CMakeLists.txt

@@ -180,8 +180,8 @@ if(ENABLE_SDL)
     ControllerInterface/SDL/SDLGamepad.cpp
     ControllerInterface/SDL/SDLGamepad.h
   )
-  target_link_libraries(inputcommon PRIVATE SDL2::SDL2)
-  target_compile_definitions(inputcommon PUBLIC HAVE_SDL2=1)
+  target_link_libraries(inputcommon PRIVATE SDL3::SDL3)
+  target_compile_definitions(inputcommon PUBLIC HAVE_SDL3=1)
 endif()
 
 if(MSVC)