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/src/slash_command/tab_command.rs

@@ -94,7 +94,7 @@ impl SlashCommand for TabSlashCommand {
                     label: path_string.clone().into(),
                     new_text: path_string,
                     replace_previous_arguments: false,
-                    run_command,
+                    after_completion: run_command.into(),
                 })
             });
 
@@ -106,7 +106,7 @@ impl SlashCommand for TabSlashCommand {
                     label: path_string.clone().into(),
                     new_text: path_string,
                     replace_previous_arguments: false,
-                    run_command,
+                    after_completion: run_command.into(),
                 });
 
             Ok(active_item_completion
@@ -115,7 +115,7 @@ impl SlashCommand for TabSlashCommand {
                     label: ALL_TABS_COMPLETION_ITEM.into(),
                     new_text: ALL_TABS_COMPLETION_ITEM.to_owned(),
                     replace_previous_arguments: false,
-                    run_command: true,
+                    after_completion: true.into(),
                 }))
                 .chain(tab_completion_items)
                 .collect())