assistant2: Use cmd-n to create a new prompt editor when already in a prompt editor (#25935)

This flips the keybindings that are used to create a new thread/prompt
editor (only when you're already in a prompt editor)

Release Notes:

- N/A

assets/keymaps/default-linux.json

@@ -612,6 +612,14 @@
       "ctrl-alt-e": "assistant2::RemoveAllContext"
     }
   },
+  {
+    "context": "AssistantPanel2 && prompt_editor",
+    "use_key_equivalents": true,
+    "bindings": {
+      "cmd-n": "assistant2::NewPromptEditor",
+      "cmd-alt-t": "assistant2::NewThread"
+    }
+  },
   {
     "context": "MessageEditor > Editor",
     "bindings": {