[FIRRTL][Verif][LTL] Replace ltl.disable with an enable folded into verif.assert

[dobios]

This PR fixes a bug in ExpandWhens that incorrectly folded the when condition into the property.
We should really have a better system than calling everything a uint1 to avoid errors like this in the future ^^"

Edit: This PR gets rid of the ltl.disable op and intrinsic in favor of having an enable operand on the verif assert like ops. This made it trivial to fix an incorrect when condition folding for AssertProperty. Most of the PR relates to fixing the chaos that was caused by removing ltl.disable.

[fabianschuiki]

We should really have a better system than calling everything a uint1 to avoid errors like this in the future ^^"

I totally agree 😀. @uenoku had some thoughts a while back on adding intrinsic types that served a similar role as intrinsic ops. Types are a lot trickier to get right though -- I remember there were a lot of concerns about a generic opaque intrinsic type. Although it would solve this particular problem here.

[dobios]

So after some discussion, this PR will shift focus towards replacing disable intrinsics with an enable that is folded into the verif intrinsics. This will make the fix in expandWhens as simple as for the other assertion type.

[uenoku]

Generally looks great! Thank you for cleaning up!

[fabianschuiki]

It's great to see ltl.disable go 🥳 Thanks for going through all this effort!

The logic of the changes looks good to me!

[darthscsi]

Generally LGTM

[uenoku]

LGTM!