Check for global blocks

Depends on GlobalBlocking change I2893b9e24173d21fe518c360f6c6add363cc7b23,
where the Block object is added to the hook.

Before this, it's only possible to check for globalblock status. It is not
possible to print a proper error message without relying on the extension
and manually calling its GlobalBlocking::getUserBlockErrors to fetch the
actual error message.

Bug: T111229
Depends-On: I2893b9e24173d21fe518c360f6c6add363cc7b23
Change-Id: I23d29c1a0e016de4e82d5b51afa94ae9afd70ee4