Use NoopTextSystem during tests (#28607)

This should allow tests to be more similar across platforms.

Release Notes:

- N/A

crates/editor/src/editor_tests.rs

@@ -1316,8 +1316,6 @@ fn test_move_cursor(cx: &mut TestAppContext) {
     });
 }
 
-// TODO: Re-enable this test
-#[cfg(target_os = "macos")]
 #[gpui::test]
 fn test_move_cursor_multibyte(cx: &mut TestAppContext) {
     init_test(cx, |_| {});