add oniguruma for regex with variable length lookbehinds (#1329)

* added pcre2 submodule

* pcre2 regex boilerplate

* tests for pcre2 regex

* flag validation, getters, construct and compile mostly working

* string escaping for source and toString(), exec, more tests

* flag sorting, match, matchAll, search, split, replace

* remove lib link

* add destructor to PCRE2RegExp

* header include

* removed ternary

* switched to oniguruma for regex library

* revert sql changes

* fix indices flag, add tests

* revert settings

* working error messages

* more tests for lastIndex, fix logic for compile and lastIndex

* move oniguruma lib to deps out dir