patch 8.2.4674: cannot force getting MouseMove events

Problem:    Cannot force getting MouseMove events.
Solution:   Add the 'mousemoveevent' option with implementaiton for the GUI.
            (Ernie Rael, closes #10044)
diff --git a/src/option.h b/src/option.h
index e344675..85f2fa8 100644
--- a/src/option.h
+++ b/src/option.h
@@ -760,6 +760,9 @@
 EXTERN int	p_mh;		// 'mousehide'
 #endif
 EXTERN char_u	*p_mousem;	// 'mousemodel'
+#ifdef FEAT_GUI
+EXTERN int	p_mousemev;	// 'mousemoveevent'
+#endif
 EXTERN long	p_mouset;	// 'mousetime'
 EXTERN int	p_more;		// 'more'
 #ifdef FEAT_MZSCHEME