[MR Widget Restructure] Merging: Show merge details in lower area

Problem

The Merging state MR Widget is still showing the pre-merge state in its lower half (including form controls, buttons, etc.).

Target

The Merging state should look like the Figma design:

Notes

There are two steps that need to happen here:

1. Show the Merge Details section instead of the "Ready to Merge" controls.
2. Move the second line of text from the top section into the Merge Details section.

See Also

• Spawning MR
• Parent Issue, specific comment