Xavierm02/streams/underlying source

[xavierm02]

Description

Implemented UnderlyingSource, and added a trivial ReadableStream constructor that only transforms its first input into an UnderlyingSource.

A few other things were added to make this possible / easier:

• A wrapper type JsFn<T, N, I, O> for JsFunction that allows to be more explicit about the JS function we expect to have, and to automatically handle the TryFromJs and IntoJs conversion for inputs and outputs.
• A Todo placeholder type for types from the spec that have not been defined yet.
• Type aliases that allow referring to some types by their WebIDL names.

Manual testing

cargo run --bin jstz -- repl
>> new ReadableStream()
thread 'main' panicked at 'not yet implemented', jstz_api/src/stream/readable/mod.rs:39:9

cargo run --bin jstz -- repl
>> new ReadableStream({type:"bytes"})
thread 'main' panicked at 'not yet implemented', jstz_api/src/stream/readable/mod.rs:39:9

cargo run --bin jstz -- repl
>> new ReadableStream({type:"invalid"})
Uncaught TypeError: invalid is not a valid value for enumeration ReadableStreamType.

One can also add

underlying_source.cancel(Some(boa_engine::js_string!("reason").into()), context);

in the constructor of ReadableStreamClass and then test it with

cargo run --bin jstz -- repl
>> >> new ReadableStream({cancel:function(reason){console.log(reason);}})
[🪵] reason
thread 'main' panicked at 'not yet implemented', jstz_api/src/stream/readable/mod.rs:42:9
Uncaught TypeError: invalid is not a valid value for enumeration ReadableStreamType.

Checklist

• Changes follow the existing code style (use make fmt-check to check)
• Tests for changes have been added
• Internal documentation has been added (if appropriate)
• Testing instructions have been added to PR

[xavierm02]

(I pushed the same thing again because the first commit had the wrong email address)

[xavierm02]

Moved to PR 254.