Required approvals message should clarify which rules are missing reviewers

Proposal

Make it easier to understand what is missing from an approval standpoint.

Today we say that "Required X from {rule}" but we don't highlight whether that approval rule has enough reviewers assigned.

One consideration is to surface "Needs reviewers" to inform the author to assign reviewers to the necessary approval rules in the enhanced reviewer assignment panel &12878 (closed).

Background problem

I find the MR approvers widget confusing. Example from this MR:

This suggested to me:

• 2 approvals are required for this MR
• 2 approvals were given since 2 faces are shown next to the words "Approved by you and others"

But that is not at all what it means. Instead it means:

• Approval from 1-N reviewers for 2 approval rules are missing

The disconnect is:

• It's not clear that the widget refers to approval rules instead of approvals (= a person clicking Approve)
• It's not clear that anything at all is actually missing

One has to scroll down to the MR blockers widget and click on the dropdown to understand what is going on, which is that 1 approval for 2 code ownership rules are missing:

I think we could improve both design and language here to make it clear that an action is required, and what this action is exactly.