Define storage operation of non-trivial StructuredSerializeForStorage records (e.g. Blob/File)

[inexorabletash]

Forked from #170

HTML's StructuredSerializeForStorage outputs "records" which are mostly plain-old-data but occasionally not, e.g. File and Blob.

@annevk points out over yonder:

... I think it's not quite an implementation-detail for File, Blob, and SharedArrayBuffer objects. E.g., does File continue to be a pointer or do we make a copy ...

(Note that we throw for SABs so that's not an issue)

I need to wrap my head around what's not covered by the monkey patching details.

(Since we're already a good bit more rigorous than "v1" I'm not considering this a blocker for "v2" for those who prefer versioned specs.)

[annevk]

This seems more like an issue for the File API, no?

[inexorabletash]

Yeah. I'll close this out.