Add more members to Regex::Options

[straight-shoota]

This is a first iteration of the enhancement of Regex::Options to decouple it from any specific libpcre values and also add more defined flags for advanced use cases as described in #13152 (comment)

[beta-ziliani]

Can't we keep the open option for PCRE? I mean, if -Duse_pcre is specified, we should strive for full backwards compatibility, including extra options.

[straight-shoota]

@beta-ziliani Actually, I'm not sure about that. While we're still supporting automatic fallback to PCRE if PCRE2 is unavailable it seems weird to have different behaviour for the -Duse_pcre flag. I'd prefer that flag to be restricted to purely selecting the library version without other implications and have only a single PCRE behaviour regardless of whether the library was selected automatically or explicitly.
Now we could consider adding an additional flag for the legacy behaviour. But I'm not sure that makes much sense due to very limited use cases.
Instead I'd prefer to focus on covering all relevant use cases in a generic way for both PCRE and PCRE2.

[beta-ziliani]

can't we simply detect the engine and act upon that?

[beta-ziliani]

I think all the issues has been addressed. Unless @Blacksmoke16 or @HertzDevil raise another issue, I consider this ready 🚀

[beta-ziliani]

related specs are failing