Allow requesting review during a rebase

[Alizter]

Problem

Picture this: A hot new PR has dropped in main and you want to rebase your patch stack, so your PRs and in-progress patches are up to date. You start rebasing and resolving conflicts, but then a team member requests a rebased version of your PR so they can merge.

Currently that team member will have to wait until you have finished rebasing so that you can rr the patch in question.

Proposal

As discussed in #280 it should be possible to show the patch stack so far. In this case, we could probably switch to the isolate branch without any issue during the rebase and rr the patches so far.