Fix shared members not being shown on members page

What does this MR do and why?

This is a continuation of !90746 (closed), not that we have proper definition of member relations on https://docs.gitlab.com/ee/user/project/members/ and https://docs.gitlab.com/ee/user/project/members/share_project_with_groups.html.

Currently, "invited group"(shared from X) members are not shown on project members page. This makes shared members be shown on the project_members page. Relates to #219230 (closed).

Specs

This mr doesn't include specs, as all the specs related to shared member have already been added on previous works of mine that at the time were being developed in parallel with this change.

Mainly: !83214 (merged) !66778 (merged)

Screenshots or screen recordings

Example, in this case, user_d has been 'invited' from group_external.
Before:
After: