settings_ui: Handle enums with fields (#37945)

Closes #ISSUE

Adds handling for Enums with fields (i.e. not `enum Foo { Yes, No }`) in
Settings UI. Accomplished by creating default values for each element
with fields (in the derive macro), and rendering a toggle button group
with a button for each variant where switching the active variant sets
the value in the settings JSON to the default for the new active
variant.

Release Notes:

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

---------

Co-authored-by: Conrad <conrad@zed.dev>

docs/src/visual-customization.md

@@ -456,7 +456,7 @@ Project panel can be shown/hidden with {#action project_panel::ToggleFocus} ({#k
     "button": true,         // Show/hide the icon in the status bar
     "dock": "right",        // Where to dock: left, right, bottom
     "default_width": 640,   // Default width (left/right docked)
-    "default_height": 320,  // Default height (bottom dockeed)
+    "default_height": 320,  // Default height (bottom docked)
   },
   "agent_font_size": 16
 ```
@@ -471,7 +471,7 @@ See [Zed AI Documentation](./ai/overview.md) for additional non-visual AI settin
     "dock": "bottom",                   // Where to dock: left, right, bottom
     "button": true,                     // Show/hide status bar icon
     "default_width": 640,               // Default width (left/right docked)
-    "default_height": 320,              // Default height (bottom dockeed)
+    "default_height": 320,              // Default height (bottom docked)
 
     // Set the cursor blinking behavior in the terminal (on, off, terminal_controlled)
     "blinking": "terminal_controlled",