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 ...

Cargo.lock

@@ -14508,6 +14508,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "assets",
+ "client",
  "command_palette_hooks",
  "editor",
  "feature_flags",
@@ -14516,9 +14517,11 @@ dependencies = [
  "gpui",
  "language",
  "menu",
+ "node_runtime",
  "paths",
  "project",
  "serde",
+ "session",
  "settings",
  "theme",
  "ui",