Rename collab_titlebar_item crate to collab_ui

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/collab_ui/src/collab_ui.rs

@@ -0,0 +1,10 @@
+mod collab_titlebar_item;
+mod contacts_popover;
+
+pub use collab_titlebar_item::CollabTitlebarItem;
+use gpui::MutableAppContext;
+
+pub fn init(cx: &mut MutableAppContext) {
+    contacts_popover::init(cx);
+    collab_titlebar_item::init(cx);
+}