Emit object for Web IDL object types

[Bashamega]

closes #2475

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged.

[saschanaz]

This will need some test against DT. I think it needed maintainer permission? @jakebailey

[jakebailey]

As in, pull into TS and then try to run it?

Probably not so easy now that we can't test nightlies on DT anymore (until that infra is reworked), but potentially still possible to an extent

[jakebailey]

I do expect this to be very breaking, however. The toJSON changes alone scare me a bit at first glance (but, I know what I said on the issue, of course)