tuple: fix hashing of integer numbers

Integer numbers stored in tuples as MP_FLOAT/MP_DOUBLE are hashed
differently from integer numbers stored as MP_INT/MP_UINT. This breaks
select() for memtx hash indexes and vinyl indexes (the latter use bloom
filters). Fix this by converting MP_FLOAT/MP_DOUBLE to MP_INT/MP_UINT
before hashing if the value can be stored as an integer. This is
consistent with the behavior of tuple comparators, which treat MP_FLOAT
and MP_INT as equal in case they represent the same number.

Closes #3907