[LLHD][SV] Unify the ProceduralRegion trait in CIRCTSupport

[fzi-hielscher]

Move the ProceduralRegion operation traits of the LLHD and SV dialects to a common declaration within the CIRCT support library. This should allow us to (temporarily) include procedural operations of one dialect under procedural regions of another dialect during lowering, without triggering an IR verification error. The behavior of the trait within the dialects remains unchanged.

We will have to further consider how the trait should work transitively.
E.g., while this is now legal:

hw.module @foo() {
  llhd.final {
      sv.write "bye"
      llhd.halt
  }
}

This still fails:

hw.module @foo(in %cond: i1) {
  llhd.final {
      scf.if %cond {
        sv.write "bye"
      }
      llhd.halt
  }
}

[fzi-hielscher]

CC #10172

[uenoku]

LGTM, do you have a plan to move ProceduralOp/NonProceduralOp traits as well?

[fzi-hielscher]

Yeah, but that's the point where I'm not sure how to do it right. I'll create a draft PR later.