Improve collab channel organization keybinds (#34821)

Change channel reorganization (move up/down) from `cmd-up/down` (mac) /
`ctrl-up/down` (linux) to `alt-up/down` (both) to match moving lines in
the editor.

Also fix an issue where if you selected channels using down/up in the
filter field, the movement shortcuts would not work (`editing` vs
`not_editing`).

Release Notes:

- N/A

assets/keymaps/default-linux.json

@@ -975,9 +975,14 @@
     "context": "CollabPanel && not_editing",
     "bindings": {
       "ctrl-backspace": "collab_panel::Remove",
-      "space": "menu::Confirm",
-      "ctrl-up": "collab_panel::MoveChannelUp",
-      "ctrl-down": "collab_panel::MoveChannelDown"
+      "space": "menu::Confirm"
+    }
+  },
+  {
+    "context": "CollabPanel",
+    "bindings": {
+      "alt-up": "collab_panel::MoveChannelUp",
+      "alt-down": "collab_panel::MoveChannelDown"
     }
   },
   {

assets/keymaps/default-macos.json

@@ -1037,9 +1037,15 @@
     "use_key_equivalents": true,
     "bindings": {
       "ctrl-backspace": "collab_panel::Remove",
-      "space": "menu::Confirm",
-      "cmd-up": "collab_panel::MoveChannelUp",
-      "cmd-down": "collab_panel::MoveChannelDown"
+      "space": "menu::Confirm"
+    }
+  },
+  {
+    "context": "CollabPanel",
+    "use_key_equivalents": true,
+    "bindings": {
+      "alt-up": "collab_panel::MoveChannelUp",
+      "alt-down": "collab_panel::MoveChannelDown"
     }
   },
   {