x11: Differentiate between mouse and keyboard focus (#13943)

Fixes https://github.com/zed-industries/zed/issues/13897

Release Notes:

- N/A

crates/gpui/src/platform/linux/x11/window.rs

@@ -450,6 +450,7 @@ impl X11WindowState {
                         xinput::XIEventMask::MOTION
                             | xinput::XIEventMask::BUTTON_PRESS
                             | xinput::XIEventMask::BUTTON_RELEASE
+                            | xinput::XIEventMask::ENTER
                             | xinput::XIEventMask::LEAVE,
                     ],
                 }],