chat panel ++ (#4044)

- Update chat panel with current channel
- Open chat panel for guests
- Open chat when joining a channel with guests
- Some tweaks for chat panels
- Don't lose focus on default panel state
- Make chat prettier (to my eyes at least)
- Fix multiple mentions in one message
- Show a border when scrolled in chat
- Fix re-docking chat panel
- Move settings subscription to dock

[[PR Description]]

Release Notes:

- Opens chat by default when joining a public channel
- Improves chat panel UI

crates/collab_ui/src/collab_panel.rs

@@ -26,7 +26,7 @@ use menu::{Cancel, Confirm, SelectNext, SelectPrev};
 use project::{Fs, Project};
 use rpc::proto::{self, PeerId};
 use serde_derive::{Deserialize, Serialize};
-use settings::{Settings, SettingsStore};
+use settings::Settings;
 use smallvec::SmallVec;
 use std::{mem, sync::Arc};
 use theme::{ActiveTheme, ThemeSettings};
@@ -254,19 +254,6 @@ impl CollabPanel {
 
             this.update_entries(false, cx);
 
-            // Update the dock position when the setting changes.
-            let mut old_dock_position = this.position(cx);
-            this.subscriptions.push(cx.observe_global::<SettingsStore>(
-                move |this: &mut Self, cx| {
-                    let new_dock_position = this.position(cx);
-                    if new_dock_position != old_dock_position {
-                        old_dock_position = new_dock_position;
-                        cx.emit(PanelEvent::ChangePosition);
-                    }
-                    cx.notify();
-                },
-            ));
-
             let active_call = ActiveCall::global(cx);
             this.subscriptions
                 .push(cx.observe(&this.user_store, |this, _, cx| {