Use a generated parser for regex validation

[desaikd]

Currently Regex needs some preprocessing done on the expression to see if this is supported by Ion Schema specificationor not.
We need to investigate on having some parser from a grammar for validating regex.

Currently, we need handwritten code for validating the regex pattern. Maybe there's a crate that we could use to generate a parser from a grammar that can validate the regex pattern (e.g. Pest). 🤷‍♂️

Originally posted by @desaikd in #96 (comment)