Document WP_Roles->role_objects as an array of WP_Role objects

[jdgrimes]

Currently the $role_objects property of the WP_Roles class is just documented as an array. It ought to be documented as an array of WP_Role objects instead: WP_Role[].

[johnbillion]

Thanks for the patch. This is effectively blocked by #41756 as the docs parser hasn't been tested with this format yet. If everything works okay and nothing explodes, we can go ahead and start implementing this known array type format for docs.

[johnbillion]

In 42870:

Docs: Document WP_Roles properties with typed array notation.

Props stevenlinx

Fixes #38732
See #41756