Unify the tasks modal and the new session modal (#31646)

Release Notes:

- Debugger Beta: added a button to the quick action bar to start a debug
session or spawn a task, depending on which of these actions was taken
most recently.
- Debugger Beta: incorporated the tasks modal into the new session modal
as an additional tab.

---------

Co-authored-by: Julia Ryan <juliaryan3.14@gmail.com>
Co-authored-by: Julia Ryan <p1n3appl3@users.noreply.github.com>
Co-authored-by: Anthony Eid <hello@anthonyeid.me>
Co-authored-by: Mikayla <mikayla@zed.dev>

assets/keymaps/default-linux.json

@@ -1019,5 +1019,12 @@
     "bindings": {
       "enter": "menu::Confirm"
     }
+  },
+  {
+    "context": "RunModal",
+    "bindings": {
+      "ctrl-tab": "pane::ActivateNextItem",
+      "ctrl-shift-tab": "pane::ActivatePreviousItem"
+    }
   }
 ]

assets/keymaps/default-macos.json

@@ -1109,5 +1109,13 @@
     "bindings": {
       "enter": "menu::Confirm"
     }
+  },
+  {
+    "context": "RunModal",
+    "use_key_equivalents": true,
+    "bindings": {
+      "ctrl-tab": "pane::ActivateNextItem",
+      "ctrl-shift-tab": "pane::ActivatePreviousItem"
+    }
   }
 ]