sys/windows: add mouse states masks

core/sys/windows/types.odin

@@ -416,6 +416,15 @@ WMSZ_BOTTOM      :: 6
 WMSZ_BOTTOMLEFT  :: 7
 WMSZ_BOTTOMRIGHT :: 8
 
+// Key State Masks for Mouse Messages
+MK_LBUTTON  :: 0x0001
+MK_RBUTTON  :: 0x0002
+MK_SHIFT    :: 0x0004
+MK_CONTROL  :: 0x0008
+MK_MBUTTON  :: 0x0010
+MK_XBUTTON1 :: 0x0020
+MK_XBUTTON2 :: 0x0040
+
 _IDC_APPSTARTING := rawptr(uintptr(32650))
 _IDC_ARROW       := rawptr(uintptr(32512))
 _IDC_CROSS       := rawptr(uintptr(32515))