Add a spamchecker callback to allow or deny room creation based on invites (#10898)

This is in the context of creating new module callbacks that modules in https://github.com/matrix-org/synapse-dinsic can use, in an effort to reconcile the spam checker API in synapse-dinsic with the one in mainline.

This adds a callback that's fairly similar to user_may_create_room except it also allows processing based on the invites sent at room creation.