I think it's time to address the elephant in the room.
This Pull Request will (hopefully!) solve part of #736.
This is a complete rewrite of `JsString`, but instead of storing `u8` bytes it stores `u16` words. The `encode!` macro (renamed to `utf16!` for simplicity) from the `const-utf16` crate allows us to create UTF-16 encoded arrays at compilation time. `JsString` implements `Deref<Target=[u16]>` to unlock the slice methods and possibly make some manipulations easier. However, we would need to create our own library of utilities for `JsString`.
So, @raskad and myself had a short discussion about the state of #736, and we came to the conclusion that it would be a good time to implement our own string interner; partly because the `string-interner` crate is a bit unmaintained (as shown by https://github.com/Robbepop/string-interner/pull/42 and https://github.com/Robbepop/string-interner/pull/47), and partly because it would be hard to experiment with custom optimizations for UTF-16 strings. I still want to thank @Robbepop for the original implementation though, because some parts of this design have been shamelessly stolen from it 😅.
Having said that, this PR is a complete reimplementation of the interner, but with some modifications to (hopefully!) make it a bit easier to experiment with UTF-16 strings, apply optimizations, and whatnot :)
José Julián Espina