Ignore an invited user

### Your use case

A user should be able to ignore / block another user who has been invited to a room, but has not joined yet.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

Start by tracing the Element iOS room-invitation and user-blocking flows to find where invited users are represented before joining. Implement support for ignoring or blocking an invited user, then verify that the user is no longer actionable in the room invitation flow and that existing blocking behavior remains unaffected.

Written by the indexing model from the issue text.