Support X11 MappingNotify events generated by user xmodmap changes

[LuisDuarte1]

Summary

When using Xorg, Zed does not update keyboard mapping when Xorg updates the keyboard mapping (MappingNotifiy event will be sent).

Example .Xmodmap:

keycode 21 = 0x3C 0x3E

Steps to trigger the problem:

1. Open Zed with normal keyboard mapping
2. Apply a modmap using xmodmap .Xmodmap
3. Zed will still use the old keyboard mapping
4. Restarting Zed will make it so that it uses the new keyboard mapping

Actual Behavior:
Uses old keyboard mapping

Expected Behavior:
To use new keyboard mapping

My workflow sometimes requires changing between keyboards of which I have slightly different keyboard layouts customized by xmodmap.

xmodmap manual pages state that a MappingNotify event will be sent to applications so that they can change they mappings, so I'm assuming that Zed does not listen to this event :)

Will try to open a PR for this :)

Zed Version and System Specs

Zed: v0.178.5 (Zed)
OS: Linux X11 ubuntu 24.04
Memory: 31 GiB
Architecture: x86_64
GPU: Intel(R) Graphics (RPL-P) || Intel open-source Mesa driver || Mesa 24.2.8-1ubuntu1~24.04.1

[LuisDuarte1]

Adding some logs to handle_event (https://github.com/zed-industries/zed/blob/main/crates/gpui/src/platform/linux/x11/client.rs#L660) seems like MappingNotify is getting filtered somewhere down the stack, maybe xim? will try to pull out the debugger for this :)

Docs state that The X server reports MappingNotify events to all clients. There is no mechanism to express disinterest in this event. so I assume that something in the stack is filtering the event.