vim-patch:9.1.1419: It is difficult to ignore all but some events (#34245)

Problem:  It is difficult to ignore all but some events.
Solution: Add support for a "-" prefix syntax in '(win)eventignore' that
          subtracts an event from the ignored set if present
          (Luuk van Baal).

8cc6d8b187

src/nvim/options.lua

@@ -2699,6 +2699,9 @@ local options = {
         Otherwise this is a comma-separated list of event names.  Example: >vim
             set ei=WinEnter,WinLeave
         <
+        To ignore all but some events, a "-" prefix can be used: >vim
+            :set ei=all,-WinLeave
+        <
       ]=],
       expand_cb = 'expand_set_eventignore',
       full_name = 'eventignore',