web_sys: Dictionaries don't have getters

[rozbb]

Describe the Bug

dictionary types from WebIDL do not have getters. You can only mutate dictionaries, and never read them. This is weird, considering how they're often used as event types or return types.

Steps to Reproduce

Example: AudioDecoderSupport has no getters, despite being defined as a return type to indicate to the caller which formats are supported. defined here has no getters

Expected Behavior

config(&self) -> AudioDecoderConfig should be a getter

set_config(&mut self, val: &AudioDecoderConfig) should be a setter

Actual Behavior

config(&mut self, val: &AudioDecoderConfig) is the only function available regarding the underlying config field, and it is a setter.

Additional Context

This is the generating code. I've dumped several hours into modifying it to generate a setter, but I've failed so far. My main issue is how do you generically convert the a JsValue from js_sys::Reflect::get into the appropriate return type? There are lots of special cases that work but it's unclear how to do this generically. E.g., how do I turn a JsValue into an Option<i32>?

Very stumped here, but willing to do work to make a PR. Please comment with pointers and I'll be on it.