Rescript-compiler: allow variant to be converted to string as well

[bobzhang]

type t = A | B  [@@bs.deriving jsConverter{string : lowercase}]

[chenglou]

I'd rather us compile like swift:

[@customCompilation]
type t =
| [@as "a"] A
| [@as "b"] B

cc @cristianoc

[hamza0867]

Hi, what about a helper function like string_of_variant at least ??

[nmn]

This has been a high priority for over a year. Is there any progress on this?

This example shows something similar is the docs, but it doesn't work.
https://bucklescript.github.io/docs/en/generate-converters-accessors#usage-5

This is an extremely important feature for inter-op between reason and existing JS code. Can we please get some progress on this! Thanks!