Add complete WebIDL for ReadableStream

[DesmondWillowbrook]

Earlier: #2373

To solve: #2252
Found this source, which is the official Streams spec.

[alexcrichton]

Thanks for the PR, but I think that this needs to update the generated code for web-sys as well?

[DesmondWillowbrook]

Oh sorry, I forgot that part! I'll do it now.

[DesmondWillowbrook]

Hey, so I followed Step 3 in the contributing guide, however, cargo gives the following error:

[~/wasm-bindgen/crates/web-sys]$ cargo run --release --package wasm-bindgen-webidl webidls src/features
error: package(s) `src/features, webidls` not found in workspace `/home/desmond/wasm-bindgen`

[alexcrichton]

I believe that's a bug in Cargo where you need -- after the wasm-bindgen-webidl argument

[DesmondWillowbrook]

Looks like it's ready to be merged!