Take advantage of BP_Groups_Group magic methods in groups component setup

[dcavins]

During single group setup in the BP Groups Component, we're doing some checks that duplicate logic done in BP_Groups_Group. We can take advantage of some of the recent work in BP_Groups_Group and simplify the single group setup.

[dcavins]

Add $is_visible and $is_user_member properties to BP_Groups_Group object. Use magic methods in BP Groups Component single group setup.

[dcavins]

In 11544:

Add $is_visible and $is_user_member properties to BP_Groups_Group object.

During single group setup in the BP_Groups_Component, we're doing
some checks that duplicate logic that is, or should be, handled in
BP_Groups_Group. Then, BP_Groups_Component can rely on
BP_Groups_Group to provide the details via recently added magic
methods.

Note: $is_user_member is an alias of $is_member for backward
compatibility.

Fixes #7494.