Simplify exclusion bit range module and type

[sim642]

Previously the exclusion bit ranges used this module:

module Interval32 = IntDomWithDefaultIkind (IntDomLifter (SOverflowUnlifter (IntervalFunctor (IntOps.Int64Ops)))) (IntIkind)

There's a lot of unnecessary complication here:

1. We're using our ikind-aware interval domain implementation for the bit ranges, which aren't really C things. And to do it we're arbitrarily considering them as C int.
2. This ikind-awareness lifts each interval domain element into a record which also keeps track of the ikind, which is always the same for bit ranges.
3. We're using our C overflow-aware interval domain and forgetting the overflow_info which isn't relevant for the small bit ranges anyway.
4. Our IntervalFunctor also has bot, but bit ranges should never have that: if the bit range is bottom, the whole def_exc/enums abstraction should become bottom.
5. For historical reasons, the bit range interval pairs are int64 * int64, but int * int would be enough for bit ranges (they're very small numbers anyway). But also it avoids extra indirection needed by int64 in OCaml.

After this PR, the module is much simpler:

module R = IntervalArith (IntOps.NIntOps)

1. IntervalArith isn't a full-blown Lattice, but just a small set of mathematical interval operations (without a bottom). This already existed before to share some code, but is slightly extended here.
2. NIntOps uses int for the bounds.

TODO

• Builds on PR Remove some unnecessary suppress_ovwarn arguments #1815.
• Merge PR Improve int domain bitwise operators, support struct bitfields #1739 before and adapt to it.