Modular bv2int part 1 (#6212)

Modular bv2int part 1 (#6212)

This PR introduces the header file for a more modular bv-to-int module, that will be called from the preprocessing pass bv-to-int, and possibly from the bit-vector solver after preprocessing.

The header file is basically a copy of the bv_to_int.h header file from preprocessing, with some adjustments to increase modularity.

In addition to the header file we also introduce an empty unit test that #includes the header, in order to identify compilation errors. The unit test will be populated in subsequent PRs, that will also include implementations.