zeta: Show keybinding in completion rating buttons in review modal (#22985)

This PR also removes the `ThumbsUp` action that wasn't being triggered
correctly. We didn't have it's counterpart `ThumbsDown`, too, so I
mostly assumed it would be harmless to remove `ThumbsUp` as well.

<img width="800" alt="Screenshot 2025-01-10 at 6 18 44 PM"
src="https://github.com/user-attachments/assets/9fd5da9f-9dff-454d-9f31-c02f1370b937"
/>

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

assets/keymaps/default-macos.json

@@ -806,7 +806,8 @@
     "context": "RateCompletionModal",
     "use_key_equivalents": true,
     "bindings": {
-      "cmd-enter": "zeta::ThumbsUp",
+      "cmd-shift-enter": "zeta::ThumbsUpActiveCompletion",
+      "cmd-shift-backspace": "zeta::ThumbsDownActiveCompletion",
       "shift-down": "zeta::NextEdit",
       "shift-up": "zeta::PreviousEdit",
       "right": "zeta::PreviewCompletion"