Part 1 of a potential 3 part series. Ref #13449
The current implementation passes key material back and forth RustCrypto
group of crates and ring. ring does not implement p521 yet.
This PR adds support for P521 named curve in `generateKey` and
`importKey` where we use RustCrypto. Other parts should be moved over to
the RustGroup group of crates for consistency.
`ZeroCopyBuf` was convenient to use, but sometimes it did hide details
that some copies were necessary in certain cases. Also it made it way to easy
for the caller to pass around and convert into different values. This commit
splits `ZeroCopyBuf` into `JsBuffer` (an array buffer coming from V8) and
`ToJsBuffer` (a Rust buffer that will be converted into a V8 array buffer).
As a result some magical conversions were removed (they were never used)
limiting the API surface and preparing for changes in #19534.
This commit cleans up the Rust side of `import_key` by using a bunch of
enums instead of structs with "type" and "data" fields.
This commit does add some duplicated code for the time being, because
a lot of the other ops still need to get the same cleanup treatment.
