* The primary purpose of pcre2_next_match() is to make it much easier for
PCRE2 clients to iterate over matches, without needing an advanced knowledge
of regular expressions.
* Secondly, we can simplify our own code by merging the three duplicate
implementations of the /g global match behaviour: pcre2demo, pcre2_substitute,
and pcre2test.
* Thirdly, as I look closely at the issue, I can improve the documentation.
* Fourthly, I would like to actually simplify the logic, removing a complex loop
which makes several match attempts, swallows duplicate matches, and more.
We can have identical behaviour with a simple retry using
PCRE2_NOTEMPTY_ATSTART.
