settings ui: Add text field support to ui layer (#37868)

This is an initial implementation that isn't used for any settings yet,
but will be used once `Vec<String>` is implemented.

I also updated the window.with_state api to grant access to a
`Context<S>` app reference instead of just an App.

## Example

<img width="603" height="83" alt="Screenshot 2025-09-09 at 2 15 56 PM"
src="https://github.com/user-attachments/assets/7b3fc350-a157-431f-a4bc-80a1806a3147"
/>


Release Notes:

- N/A

assets/keymaps/default-linux.json

@@ -341,7 +341,7 @@
       "enter": "agent::Chat",
       "shift-ctrl-r": "agent::OpenAgentDiff",
       "ctrl-shift-y": "agent::KeepAll",
-      "ctrl-shift-n": "agent::RejectAll",
+      "ctrl-shift-n": "agent::RejectAll"
     }
   },
   {