Serializable types should include unrestricted double and unrestricted float

[samweinig]

Currently, the list of serializable types (https://heycam.github.io/webidl/#dfn-serializable-type) does not include unrestricted double and unrestricted float. Specs are relying on them being serializable (see https://drafts.fxtf.org/geometry-1/#dompointreadonly for an example), so it would probably make sense to add.

[domenic]

This appears to be fixed by #323:

https://s3.amazonaws.com/pr-preview/tobie/webidl/tojson.html#dfn-json-types