- `JsString::from_code_point` - allows to create JS strings using slice of codes in WASM memory.
- `JsString::from_char_code` - same as above, but also uses updated signature with `u16` instead of `u32` (partially helps with #1460 at least for the new binding).
This commit aims to address #1348 via a number of strategies:
* Documentation is updated to warn about UTF-16 vs UTF-8 problems
between JS and Rust. Notably documenting that `as_string` and handling
of arguments is lossy when there are lone surrogates.
* A `JsString::is_valid_utf16` method was added to test whether
`as_string` is lossless or not.
The intention is that most default behavior of `wasm-bindgen` will
remain, but where necessary bindings will use `JsString` instead of
`str`/`String` and will manually check for `is_valid_utf16` as
necessary. It's also hypothesized that this is relatively rare and not
too performance critical, so an optimized intrinsic for `is_valid_utf16`
is not yet provided.
Closes#1348
