[F.Rq.] Mem. domain "translation", hint when using a mirror

[YoshiRulz]

First, the watch edit dialog should have a button to add the sysbus offset and set the domain to the sysbus, or vice-versa if it's already in the sysbus domain. The UI should be easy, but it relies on cores (managed side probably) surfacing that offset information.

Second, for many systems/mappers, there are multiple "mirrored" copies of blocks. We should also surface that information somehow, for example by displaying a warning in RAM Watch and/or the watch editor.

see also #462, #1700