Add Regex API which returns RzIterator instead of PVectors.

[Rot127]

Is your feature request related to a problem? Please describe.

The regex API currently allocates RzPVectors and RzRegexMatch. This is of course not optional. Because we could save the allocations. PCRE2 itself doesn't allocate its matches.

Describe the solution you'd like

Instead we should add an implementation which returns an RzIterator.
The RzIterator->next could just do the pcre2_match(), increment the offset into the buffer and return the RzRegexMatch object over the stack.
In the end RzRegexMatch is rather small.

One problem is grouping of multiple matches per buffer. Implementing match_all requires an additional index. To indicate where each RzRegexMatch belongs to.

Regex: "(Te(x)t)"
Possible groups: 0: (Text) 1: (x)

Match all on: "TextTextText"

Gives: 
[
{0: Text, 1: x},
{0: Text, 1: x},
{0: Text, 1: x},
]

For our match_all implementation with RzIterators, we somehow have to get the indices for each {0: Text, 1: x}.

Describe alternatives you've considered

None

Additional context
...