Respect NODE_PRESERVE_SYMLINKS and possibly other appropriate environment variables?

[attakorns]

Hi there,

First things first, I have to say I've been using this module and am loving it! Thank you for all the hard work to put this fantastic module together!

I got an feature request: I just found out today that even though esm does respect the --preserve-symlinks flag, it does not respect NODE_PRESERVE_SYMLINKS environment variable. A quick fix in get-flags.js can be made to support this (and I don't know, maybe other environment variables that affects module loading that esm should respect too?)

I will be more than happy to contribute however I am an absolute newbie and have never contributed to a project on github before so I'm afraid I might break things instead?!

That's all, and thank you for this module again!