xinput improvements

*make LB/RB aliases for LS/RS
*support LSB/RSB (thumbstick buttons)
*move some duplicated code into a function
*add button name comments to keyconfig

source/plugins/TLAC/Input/Xinput/Xinput.h

@@ -45,5 +45,7 @@ namespace TLAC::Input
 		FLOAT keyIntervalTapTimes[0xFF];
 
 		static Xinput* instance;
+
+		void SetTapStates(BYTE keycode, float elapsed);
 	};
 }