vim: Fix :wq in multibuffer (#24603)

Supercedes #24561
Closes #21059

Before this change we would skip saving multibuffers regardless of the
save intent. Now we correctly save them.

Along the way:
* Prompt to save when closing the last singleton copy of an item (even
if it's still open in a multibuffer).
* Update our file name prompt to pull out dirty project items from
multibuffers instead of counting multibuffers as untitled files.
* Fix our prompt test helpers to require passing the button name instead
of the index. A few tests were passing invalid responses to save
prompts.
* Refactor the code a bit to hopefully clarify it for the next bug.

Release Notes:

- Fixed edge-cases when closing multiple items including multibuffers.
Previously no prompt was generated when closing an item that was open in
a multibuffer, now you will be prompted.
- vim: Fix :wq in a multibuffer

crates/zed/src/zed.rs

@@ -2061,7 +2061,7 @@ mod tests {
             .unwrap();
         executor.run_until_parked();
 
-        cx.simulate_prompt_answer(1);
+        cx.simulate_prompt_answer("Don't Save");
         close.await.unwrap();
         assert!(!window_is_edited(window, cx));
 
@@ -2122,7 +2122,7 @@ mod tests {
         assert_eq!(cx.update(|cx| cx.windows().len()), 1);
 
         // The window is successfully closed after the user dismisses the prompt.
-        cx.simulate_prompt_answer(1);
+        cx.simulate_prompt_answer("Don't Save");
         executor.run_until_parked();
         assert_eq!(cx.update(|cx| cx.windows().len()), 0);
     }
@@ -2857,7 +2857,7 @@ mod tests {
             })
             .unwrap();
         cx.background_executor.run_until_parked();
-        cx.simulate_prompt_answer(0);
+        cx.simulate_prompt_answer("Overwrite");
         save_task.await.unwrap();
         window
             .update(cx, |_, _, cx| {
@@ -3156,7 +3156,7 @@ mod tests {
             },
         );
         cx.background_executor.run_until_parked();
-        cx.simulate_prompt_answer(1);
+        cx.simulate_prompt_answer("Don't Save");
         cx.background_executor.run_until_parked();
 
         window