Introduce dynamic tab titles for unsaved files based on buffer content (#32353)

https://github.com/user-attachments/assets/0bb08784-251c-4221-890a-2d6b3fb94e0f

For new, unsaved files:

- If a buffer has no content, or contains only whitespace, use
`untitled`
- If a buffer has content, take the first 40 chars of the first line

| Sublime | VS Code | Zed |
|---------|---------|-----|
| <img width="227" alt="SCR-20250608-ouux"
src="https://github.com/user-attachments/assets/d02b1e50-5775-4252-86e6-6c9d3f6c72fb"
/> | <img width="230" alt="SCR-20250608-ousn"
src="https://github.com/user-attachments/assets/7c9c016b-642f-4a80-9bc1-8c9bdc7bbd32"
/> | <img width="242" alt="SCR-20250608-ovbg"
src="https://github.com/user-attachments/assets/c7f4be5c-5bba-4a2a-b477-1392ca938cd5"
/> |

Note that this implementation also trims all leading whitespace, so that
if the buffer has any non-whitespace content, we use it. VS Code and
Sublime do not do this.

| Sublime | VS Code | Zed |
|---------|---------|-----|
| <img width="233" alt="SCR-20250608-oviq"
src="https://github.com/user-attachments/assets/ccffecc6-0f46-4d1b-8739-740240bc067b"
/> | <img width="198" alt="SCR-20250608-ovkq"
src="https://github.com/user-attachments/assets/35c20149-f898-417b-aff3-dda22b8cc1f3"
/> | <img width="233" alt="SCR-20250608-ovns"
src="https://github.com/user-attachments/assets/2509e8f6-254b-4fcb-a0ea-e18e95bb685b"
/> |

Release Notes:

- Introduced dynamic tab titles for unsaved files based on buffer
content

crates/editor/src/editor.rs

@@ -18791,6 +18791,11 @@ impl Editor {
                 cx.emit(EditorEvent::BufferEdited);
                 cx.emit(SearchEvent::MatchesInvalidated);
                 if *singleton_buffer_edited {
+                    if let Some(buffer) = multibuffer.read(cx).as_singleton() {
+                        if buffer.read(cx).file().is_none() {
+                            cx.emit(EditorEvent::TitleChanged);
+                        }
+                    }
                     if let Some(project) = &self.project {
                         #[allow(clippy::mutable_key_type)]
                         let languages_affected = multibuffer.update(cx, |multibuffer, cx| {