Add support for various action keys to Linux keymap (#22997)

Adds support for Cut, Copy, Paste, Undo, Redo, New, Open, Save, and Find
keys to the default keymap. These keys can be found on old keyboards,
but also custom layouts like
[Extend](https://dreymar.colemak.org/layers-extend.html).

Release Notes:

- Added support for the Cut, Copy, Paste, Undo, Redo, New, Open, Save,
and Find keys to the default keymap.

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

@@ -698,6 +698,12 @@ impl crate::Keystroke {
             Keysym::KP_Next => "pagedown".to_owned(),
             Keysym::XF86_Back => "back".to_owned(),
             Keysym::XF86_Forward => "forward".to_owned(),
+            Keysym::XF86_Cut => "cut".to_owned(),
+            Keysym::XF86_Copy => "copy".to_owned(),
+            Keysym::XF86_Paste => "paste".to_owned(),
+            Keysym::XF86_New => "new".to_owned(),
+            Keysym::XF86_Open => "open".to_owned(),
+            Keysym::XF86_Save => "save".to_owned(),
 
             Keysym::comma => ",".to_owned(),
             Keysym::period => ".".to_owned(),