MR Review Panel: Improve review submission form layout

Context

In the context of the wider effort to build an improved MR Review Panel as described in &14651 and #474794, this is step 1.

• Step 1: Review bar ⬅️ this issue (#525839 (closed))
• Step 2: New drawer to preview Review pending comments (#525841 (closed))
• Step 3-?: Iterate on improving drawer (future issues)

This issue covers the improving of the form used to submit a review (after clicking Finish Review)

Tasks

1. Change radio buttons and submit into 3 buttons
   1. Approve
      • Tooltip: "Submit feedback and approve this merge request."
   2. Request changes
      • Tooltip: "Submit feedback that should be addressed before merging."
   3. Comment
      • Tooltip: "Submit feedback without explicit approval."
2. Move delete pending comments button into the review popover

Mockup

Figma

Before	After (this issue)

Implementation plan

These changes can be shipped independently of the other issues (listed in the context section of this description). (to be confirmed by @mle)