linux: Fix buttons clicks wouldn’t work on startup until clicked on center pane (#34590)

Closes #31805

This is an issue with Linux currently that `window.focus` is `None` upon
startup in both X11 and Wayland. Specifically, the order in which
[this](8d05a3d389/crates/gpui/src/window.rs (L3116))
and
[this](8d05a3d389/crates/gpui/src/app.rs (L956))
are executed varies between Linux and macOS. That is, one tries to
remove (blur) focus from a window, while other checks window focus to
put that focus id to a frame. In macOS, blur happens afterwards setting
focus on a frame, but in Linux, the inverse of it happens, leading to
`window.focus` to `None`.

For the time being, we handle all visible buttons to take care of this
**focus can be `None`** case, and make it work anyway. But, we should
look at the deeper issue mentioned above with GPUI. Created new issue to
track that https://github.com/zed-industries/zed/issues/34591.

Release Notes:

- Fixed an issue where button clicks wouldn’t work on startup until
clicked on the center pane on Linux.

crates/workspace/src/dock.rs

@@ -873,6 +873,8 @@ impl Render for PanelButtons {
                     (action, icon_tooltip.into())
                 };
 
+                let focus_handle = dock.focus_handle(cx);
+
                 Some(
                     right_click_menu(name)
                         .menu(move |window, cx| {
@@ -909,6 +911,7 @@ impl Render for PanelButtons {
                                 .on_click({
                                     let action = action.boxed_clone();
                                     move |_, window, cx| {
+                                        window.focus(&focus_handle);
                                         window.dispatch_action(action.boxed_clone(), cx)
                                     }
                                 })