Preserve original regexp flags order

[silentroach]

Regexp flags order isn't important, so it is better to use real regexp instead of its string representation.

/foo/mig.toString() = /foo/gim

[silentroach]

without this fix it will be error here with optimized regexp /foo/gim

[BrainMaestro]

Hey @silentroach. Thanks for the PR.
Looks like this introduces a separate feature to handle and warn of invalid regexes which is great.

One question though, is preserving the flag order really necessary? Having all regex flags in a project follow a particular order might be a good thing right? On the other hand, it introduces a lot of unnecessary warnings.

[silentroach]

Yep, the original reason for this pr is to remove this unneccessary warnings. In big project with tons of regexps it isn't great to replace all regexps with the same one, but with other flags order :}

[BrainMaestro]

Yeah I figured. One more thing, can you add a test for the case of parsing failing?

[silentroach]

Here is an example of regexps that can't be parsed: / ([.|,])/g, /[\n|\t]/ig

But it is a regexp-tree bug, I will try to fix it later (or report). There is no reason to test it here though.

[BrainMaestro]

Okay. Thanks!