Add editor: convert to sentence case (#35015)

This PR adds an `editor: convert to sentence case` action.

I frequently find myself copying branch names and then removing the
hyphens and ensuring the first letter is capitalized, and then using the
result text for the commit message.

For example:

<img width="927" height="482" alt="image"
src="https://github.com/user-attachments/assets/adf14a37-a92e-44df-8c0e-267b5c7677fb"
/>

You can achieve this with a combination of other text manipulation
commands, but this action makes it even easier.

Also, moved `toggle_case` down into the area where all other commands
internally using `manipulate_text` are located.

Release Notes:

- Added `editor: convert to sentence case`

crates/editor/src/editor_tests.rs

@@ -4724,6 +4724,23 @@ async fn test_toggle_case(cx: &mut TestAppContext) {
     "});
 }
 
+#[gpui::test]
+async fn test_convert_to_sentence_case(cx: &mut TestAppContext) {
+    init_test(cx, |_| {});
+
+    let mut cx = EditorTestContext::new(cx).await;
+
+    cx.set_state(indoc! {"
+        «implement-windows-supportˇ»
+    "});
+    cx.update_editor(|e, window, cx| {
+        e.convert_to_sentence_case(&ConvertToSentenceCase, window, cx)
+    });
+    cx.assert_editor_state(indoc! {"
+        «Implement windows supportˇ»
+    "});
+}
+
 #[gpui::test]
 async fn test_manipulate_text(cx: &mut TestAppContext) {
     init_test(cx, |_| {});