Require accepting ToS when enabling zeta (#23255)

Note: Design hasn't been reviewed yet, but the logic is done

When the user switches the inline completion provider to `zed`, we'll
show a modal prompting them to accept terms if they haven't done so:


https://github.com/user-attachments/assets/3fc6d368-c00a-4dcb-9484-fbbbb5eb859e

If they dismiss the modal, they'll be able to get to it again from the
inline completion button:


https://github.com/user-attachments/assets/cf842778-5538-4e06-9ed8-21579981cc47

This also stops zeta sending requests that will fail immediately when
ToS are not accepted.

Release Notes:

- N/A

---------

Co-authored-by: Richard <richard@zed.dev>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
Co-authored-by: Joao <joao@zed.dev>

assets/keymaps/default-macos.json

@@ -875,5 +875,12 @@
       "cmd-shift-enter": "zeta::ThumbsUpActiveCompletion",
       "cmd-shift-backspace": "zeta::ThumbsDownActiveCompletion"
     }
+  },
+  {
+    "context": "ZedPredictTos",
+    "use_key_equivalents": true,
+    "bindings": {
+      "escape": "menu::Cancel"
+    }
   }
 ]