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/runtime/doc/options.txt b/runtime/doc/options.txt
index bdc2522..d5e5e68 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5517,6 +5517,18 @@
 
 	The 'mousemodel' option is set by the |:behave| command.
 
+						*'mousemoveevent'* *'mousemev'*
+'mousemoveevent' 'mousemev'  boolean	(default off)
+			global
+			{only works in the GUI}
+	When on, mouse move events are delivered to the input queue and are
+	available for mapping. The default, off, avoids the mouse movement
+	overhead except when needed. See |gui-mouse-mapping|.
+	Warning: Setting this option can make pending mappings to be aborted
+	when the mouse is moved.
+	Currently only works in the GUI, may be made to work in a terminal
+	later.
+
 					*'mouseshape'* *'mouses'* *E547*
 'mouseshape' 'mouses'	string	(default "i-r:beam,s:updown,sd:udsizing,
 					vs:leftright,vd:lrsizing,m:no,