Factorize input hooks into reusable monitor classes

Those monitors will need some context so this will be useful
in the nearby future.

src/duckstation-qt/CMakeLists.txt

@@ -55,6 +55,8 @@ set(SRCS
   inputbindingdialog.cpp
   inputbindingdialog.h
   inputbindingdialog.ui
+  inputbindingmonitor.cpp
+  inputbindingmonitor.h
   inputbindingwidgets.cpp
   inputbindingwidgets.h
   main.cpp