Add binding for IEEE-754 bit-vector to FPA

[KpwnZ]

This PR exposes the Z3_mk_fpa_to_fp_bv() API which is useful for interpreter memory model.

[toolCHAINZ]

Thanks for the contribution! Could you add some unit tests for these new APIs? I think it would be particularly helpful for library users to see the usage of from_ieee_bv. I'm a little on the fence about that one; it is good to support the full bredth of floating point types Z3 can operate on, but I think most users will be using the 32 or 64 bit variants. So I worry a little about which one people will find first. I wish that there was a way to tighten the types on that API (e.g. the Sort has to be a Float Sort), but that doesn't seem possible with how z3.rs currently represents Sorts.

For the other two APIs, I think it would be pretty slick to show a round-trip betwen Floats and BVs using the existing Float::to_ieee_bv impl and as_f64.