patch 9.0.1084: code handling low level MS-Windows events cannot be tested

Problem:    Code handling low level MS-Windows events cannot be tested.
Solution:   Add test_mswin_event() and tests using it. (Christopher Plewright,
            closes #11622)
diff --git a/src/testdir/test_gui.vim b/src/testdir/test_gui.vim
index 3c7cfb9..0c1e0a5 100644
--- a/src/testdir/test_gui.vim
+++ b/src/testdir/test_gui.vim
@@ -1281,7 +1281,7 @@
     let g:eventlist = g:eventlist[1 : ]
   endif
 
-  call assert_equal([#{row: 4, col: 31}, #{row: 11, col: 31}], g:eventlist)
+  call assert_equal([#{row: 3, col: 30}, #{row: 10, col: 30}], g:eventlist)
 
   " wiggle the mouse around within a screen cell, shouldn't trigger events
   call extend(args, #{cell: v:false})
@@ -1638,10 +1638,10 @@
 " Test for sending low level key presses
 func SendKeys(keylist)
   for k in a:keylist
-    call test_gui_event("sendevent", #{event: "keydown", keycode: k})
+    call test_gui_event("key", #{event: "keydown", keycode: k})
   endfor
   for k in reverse(a:keylist)
-    call test_gui_event("sendevent", #{event: "keyup", keycode: k})
+    call test_gui_event("key", #{event: "keyup", keycode: k})
   endfor
 endfunc