[UX] Display php error messages in a dedicated block so we can limit visibility per role.

This is a follow-up of #2138, which in turn is a follow-up of #2040...

There is already a respective issue filed against D8 core: Option to display php error messages in a block so we can limit visibility per role [#2743119]

At /admin/config/development/logging we have no option to display php error messages in a block that would enable admins limiting the display of error messages per role. Such a feature would be invaluable for debugging. Currently, we cannot control who sees the error messages, but in a block we could easily limit visibility per role.