Support generation of latches

### Motivation

There are some scenarios where creating latches is valuable (`always_latch`).

### Desired solution

Add a way to generate latches to ROHD. Perhaps as a sibling or configuration of `Sequential`.

### Alternatives considered

Ban latches. This is effectively the current answer, but may be overly restrictive.

### Additional details

Detection of latch hardware may be a part of this (see https://github.com/intel/rohd/issues/285).

Thought should be put in to how to make latches as safe as possible to deal with.