gpui: Small tab group performance improvements (#41885)

Closes #ISSUE

Removes a few eager container clones and iterations.

Added a todo to `get_prev_tab_group_window` and
`get_next_tab_group_window`. They seem to use `HashMap::keys()` for
choosing the previous tab group, however `.keys()` returns an arbitrary
order, so I'm not sure if previous actually means anything here. Conrad
seems to have worked on this part previously, maybe he has some
insights. That can possibly be a follow-up PR, but I'd be willing to
work on it here as well since the other changes are so simple.

Release Notes:

- N/A

crates/gpui/src/app.rs

@@ -316,6 +316,7 @@ impl SystemWindowTabController {
             .find_map(|(group, tabs)| tabs.iter().find(|tab| tab.id == id).map(|_| group));
 
         let current_group = current_group?;
+        // TODO: `.keys()` returns arbitrary order, what does "next" mean?
         let mut group_ids: Vec<_> = controller.tab_groups.keys().collect();
         let idx = group_ids.iter().position(|g| *g == current_group)?;
         let next_idx = (idx + 1) % group_ids.len();
@@ -340,6 +341,7 @@ impl SystemWindowTabController {
             .find_map(|(group, tabs)| tabs.iter().find(|tab| tab.id == id).map(|_| group));
 
         let current_group = current_group?;
+        // TODO: `.keys()` returns arbitrary order, what does "previous" mean?
         let mut group_ids: Vec<_> = controller.tab_groups.keys().collect();
         let idx = group_ids.iter().position(|g| *g == current_group)?;
         let prev_idx = if idx == 0 {
@@ -361,12 +363,9 @@ impl SystemWindowTabController {
 
     /// Get all tabs in the same window.
     pub fn tabs(&self, id: WindowId) -> Option<&Vec<SystemWindowTab>> {
-        let tab_group = self
-            .tab_groups
-            .iter()
-            .find_map(|(group, tabs)| tabs.iter().find(|tab| tab.id == id).map(|_| *group))?;
-
-        self.tab_groups.get(&tab_group)
+        self.tab_groups
+            .values()
+            .find(|tabs| tabs.iter().any(|tab| tab.id == id))
     }
 
     /// Initialize the visibility of the system window tab controller.
@@ -441,7 +440,7 @@ impl SystemWindowTabController {
     /// Insert a tab into a tab group.
     pub fn add_tab(cx: &mut App, id: WindowId, tabs: Vec<SystemWindowTab>) {
         let mut controller = cx.global_mut::<SystemWindowTabController>();
-        let Some(tab) = tabs.clone().into_iter().find(|tab| tab.id == id) else {
+        let Some(tab) = tabs.iter().find(|tab| tab.id == id).cloned() else {
             return;
         };
 
@@ -504,16 +503,14 @@ impl SystemWindowTabController {
             return;
         };
 
+        let initial_tabs_len = initial_tabs.len();
         let mut all_tabs = initial_tabs.clone();
-        for tabs in controller.tab_groups.values() {
-            all_tabs.extend(
-                tabs.iter()
-                    .filter(|tab| !initial_tabs.contains(tab))
-                    .cloned(),
-            );
+
+        for (_, mut tabs) in controller.tab_groups.drain() {
+            tabs.retain(|tab| !all_tabs[..initial_tabs_len].contains(tab));
+            all_tabs.extend(tabs);
         }
 
-        controller.tab_groups.clear();
         controller.tab_groups.insert(0, all_tabs);
     }