Support complex Regexes

[npatki]

Problem Description

Initially described in issue #2208: the RegexGenerator does not currently support all types of regexes. In particular, it does not support regexes with sub-patterns ("or" logic). This is described in detail in this FAQ.

Expected behavior

It would be nice to add support for regexes with sub-patterns. Eg. ([A-Z]{2}|\d{4}) (example from the docs FAQ) or ^(?=.{3,255}$)[a-zA-Z0-9][-a-zA-Z0-9]{0,62}(\.[a-zA-Z0-9][-a-zA-Z0-9]{0,62})*$ (example from issue 2208).