Should we make a StaticallyComputableWidth Type interface and get hw::getBitWidth to use it? Or potentially replace it?

The use case here is one might have a hw.struct with a field which is not a hw type. (As I do with ESI's Window type.) At a minimum, hw.bitcast compares the two bitwidths. While said field would not be able to be lowered directly to SystemVerilog though it may get lowered of removed by a later pass.

IIRC we've always said that the HW dialect should be as open as possible, this is something which isn't terribly open. I seem to recall having this discussion in the past...

What do people think?