Security definer views don't work with engine's privilege checks

This is a follow-up for MDEV-7574.

Different engines check user privileges for some reasons. For example, InnoDB and XtraDB often check PROCESS privilege in the I_S code.

All these checks always use invoker's privileges, and don't respect SQL SECURITY DEFINER of views.

We should extract the fix for MDEV-7574 from the CONNECT code and make it into an easy to use function that all plugins can use. And change plugins to use it.