settings_ui: Collect all settings files (#38816)

Closes #ISSUE

Updates the settings editor to collect all known settings files from the
settings store, in order to show them in the UI. Additionally adds a
fake worktree instantiation in the settings UI example binary in order
to have more than one file available when testing.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/session/src/session.rs

@@ -43,7 +43,7 @@ impl Session {
         }
     }
 
-    #[cfg(any(test, feature = "test-support"))]
+    // #[cfg(any(test, feature = "test-support"))]
     pub fn test() -> Self {
         Self {
             session_id: Uuid::new_v4().to_string(),