Fix more bugs in files (#16241)

Fixes:
- [x] an issue where directories would only match by prefix, causing
both a directory and a file to be matched if in the same directory
- [x] An issue where you could not continue a file completion when
selecting a directory, as `tab` on a file would always run the command.
This effectively disabled directory sub queries.
- [x] Inconsistent rendering of files and directories in the slash
command

Release Notes:

- N/A

---------

Co-authored-by: max <max@zed.dev>

crates/project/src/project_tests.rs

@@ -5204,7 +5204,7 @@ async fn search(
         .collect())
 }
 
-fn init_test(cx: &mut gpui::TestAppContext) {
+pub fn init_test(cx: &mut gpui::TestAppContext) {
     if std::env::var("RUST_LOG").is_ok() {
         env_logger::try_init().ok();
     }