Handle Permissions for Group Sharing with Pending Memberships

What does this MR do and why?

This MR treats pending members of groups invited to other groups as if they are not members for permissions purposes.

It is broken out from !75554 (closed) and is part of the work for #332598 (closed) to handle permissions for pending memberships.

Issue: #332598 (closed)

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.