Sqlean PCRE2-based regexp extensions

[saaj]

Build Sqlean's regexp extension based on PCRE2.

It's +42% in build size:

- sql-wasm.wasm 742158
+ sql-wasm.wasm 1054448

And requires EMULATE_FUNCTION_POINTER_CASTS (more details on it) which is undesired for performance reasons.
Benchmark doesn't show much slowdown though:

master	firefox 115	select	0.15 s ± 1.5%
pr	firefox 115	select	0.16 s ± 1.2%
master	chromium 128	select	0.14 s ± 1.4%
pr	chromium 128	select	0.14 s ± 1.4%
master	firefox 115	import	0.93 s ± 1.8%
pr	firefox 115	import	0.91 s ± 1.5%
master	chromium 128	import	1.26 s ± 1.5%
pr	chromium 128	import	1.26 s ± 1.5%

result-analysis.pdf

[saaj]

Close in favour of lana-k#118.