vim-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 vim/vim#10044)
c4cb544cd5

This only ports the docs and the option variable.
The following commits will actually implement it as a UI option.

runtime/doc/options.txt

@@ -4231,6 +4231,18 @@ A jump table for the options with a short description can be found at |Q_op|.
 
 	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.
+	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.
+
 						*'mousescroll'*
 'mousescroll'		string	(default "ver:3,hor:6")
 			global

src/nvim/option_defs.h

@@ -616,6 +616,7 @@ EXTERN int p_ma;                ///< 'modifiable'
 EXTERN int p_mod;               ///< 'modified'
 EXTERN char *p_mouse;           // 'mouse'
 EXTERN char *p_mousem;          // 'mousemodel'
+EXTERN int p_mousemev;          ///< 'mousemoveevent'
 EXTERN int p_mousef;            // 'mousefocus'
 EXTERN char *p_mousescroll;     // 'mousescroll'
 EXTERN long p_mousescroll_vert INIT(= MOUSESCROLL_VERT_DFLT);

src/nvim/options.lua

@@ -1621,6 +1621,13 @@ return {
       varname='p_mousem',
       defaults={if_true="popup_setpos"}
     },
+    {
+      full_name='mousemoveevent', abbreviation='mousemev',
+      short_desc=N_("deliver mouse move events to input queue"),
+      type='bool', scope={'global'},
+      varname='p_mousemev',
+      defaults={if_true=false}
+    },
     {
       full_name='mousescroll',
       short_desc=N_("amount to scroll by when scrolling with a mouse"),