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/assistant_slash_command/src/assistant_slash_command.rs

@@ -15,6 +15,35 @@ pub fn init(cx: &mut AppContext) {
     SlashCommandRegistry::default_global(cx);
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum AfterCompletion {
+    /// Run the command
+    Run,
+    /// Continue composing the current argument, doesn't add a space
+    Compose,
+    /// Continue the command composition, adds a space
+    Continue,
+}
+
+impl From<bool> for AfterCompletion {
+    fn from(value: bool) -> Self {
+        if value {
+            AfterCompletion::Run
+        } else {
+            AfterCompletion::Continue
+        }
+    }
+}
+
+impl AfterCompletion {
+    pub fn run(&self) -> bool {
+        match self {
+            AfterCompletion::Run => true,
+            AfterCompletion::Compose | AfterCompletion::Continue => false,
+        }
+    }
+}
+
 #[derive(Debug)]
 pub struct ArgumentCompletion {
     /// The label to display for this completion.
@@ -22,7 +51,7 @@ pub struct ArgumentCompletion {
     /// The new text that should be inserted into the command when this completion is accepted.
     pub new_text: String,
     /// Whether the command should be run when accepting this completion.
-    pub run_command: bool,
+    pub after_completion: AfterCompletion,
     /// Whether to replace the all arguments, or whether to treat this as an independent argument.
     pub replace_previous_arguments: bool,
 }