X11: Don't emit keypress events for modifiers (#10271)

This fixes certain shortcuts/motions on X11 like in vim mode "v i )",
where previously zed would interpret it as "v i SHIFT )" due to the x11
backend emitting key press events for modifier keys even though other
platforms like Wayland don't. This also adds support for
ModifiersChanged events to X11

Release Notes:

- Fixed vim motions like "v i )" not working on X11
([#10199](https://github.com/zed-industries/zed/issues/10199)).

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

@@ -624,6 +624,24 @@ impl Keystroke {
     }
 }
 
+impl Modifiers {
+    pub(super) fn from_xkb(keymap_state: &State) -> Self {
+        let shift = keymap_state.mod_name_is_active(xkb::MOD_NAME_SHIFT, xkb::STATE_MODS_EFFECTIVE);
+        let alt = keymap_state.mod_name_is_active(xkb::MOD_NAME_ALT, xkb::STATE_MODS_EFFECTIVE);
+        let control =
+            keymap_state.mod_name_is_active(xkb::MOD_NAME_CTRL, xkb::STATE_MODS_EFFECTIVE);
+        let platform =
+            keymap_state.mod_name_is_active(xkb::MOD_NAME_LOGO, xkb::STATE_MODS_EFFECTIVE);
+        Modifiers {
+            shift,
+            alt,
+            control,
+            platform,
+            function: false,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;