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.

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"),