Use 'std::vector' to store closure items during determinization.

Use 'std::vector' to store closure items during determinization.

This makes code somewhat clearer compared to using plain C arrays:
all function accept one parameter (vector) instead of two (array
start, array end/array length).

However, vectors have nontrivial structure and 'ord_hash_set_t'
is not suitable for them. That's why instead of 'ord_hash_set_t'
we now use 'lookup_t': just like 'ord_hash_set_t' it has constant
random access ang logarithmic insertion complexity, but unike
'ord_hash_set_t' it is not meant to be a container (rather an index).