Merge quick_action_bar into zed (#21026)

This PR merges the `quick_action_bar` crate into the `zed` crate.

We weren't really gaining anything by having it be a separate crate, and
it was introducing an additional step in the dependency graph that was
getting in the way.

It's only ~850 LOC, so the impact on the compilation speed of the `zed`
crate itself is negligible.

Release Notes:

- N/A

crates/zed/src/zed.rs

@@ -6,6 +6,7 @@ pub(crate) mod linux_prompts;
 #[cfg(target_os = "macos")]
 pub(crate) mod mac_only_instance;
 mod open_listener;
+mod quick_action_bar;
 #[cfg(target_os = "windows")]
 pub(crate) mod windows_only_instance;