Unrecursified and merged bv::utils::is(Core|Equality)Term. (#1605)

Unrecursified and merged bv::utils::is(Core|Equality)Term. (#1605)

This unrecursifies and merges bv::utils::isCoreTerm and bv::utils::isEqualityTerm to avoid
code duplication.

In the best case, the recursive implementation visits less nodes. This can be achieved with
the non-recursive implementation, however, at the cost of increased code complexity.
In practice, on QF_BV the new implementation slightly improves performance.

Tested against the recursive implementation with a temporary assertion on regression
tests (bv::utils::isCoreTerm was tested with --bv-eq-slicer=auto).
Further tested on QF_BV with a TO of 300s (slight performance improvement).