xref. https://github.com/github/accessibility-audits/issues/5715

Description

This PR sits on top of #17671 and, with @tidy-dev 's help, improves the look & feel and aria semantics of the reorder commits hint by:

• Not displaying the hint as a balloon (although still keeping rounded corners to make it slightly different from the other elements on the screen)
• Showing a title in the hint for extra context
• Use key icons instead of text. I chose to replace the text with the icons to keep the verbiage short (and I think it looks nice too 😳)
• Also adapt verbiage for screen readers ("choose new location" instead of "move commits")
• Remove dialog aria semantics from this specific popover

Screenshots

Release notes

Notes: no-notes