Update Merge Request list approvals / approvers to be more clear

What does this MR do?

For #213435 (closed)

This MR updates the Merge Request list approvals widget to be more clear per the new designs in #213435 (closed).

In broad strokes:

• The tooltip shows "required approvals", not just "approvals".
• The text of the element shows the number of required approvals remaining
• The tooltip shows the total numbers of approvers once the MR is approved
• The tooltip (and the icon, unchanged from the previous version) shows whether the current user has approved the MR.

Screenshots

Total Approvers Needed	Self-Approved	Approved	Unapproved	Unapproved (self-approved)
1				-
2+

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team