Instead of just putting in members directly, wrap them up in structs
which represent what a URL blob entry is meant to hold per the spec.
This makes more obvious what this is meant to represent, such as the
ByteBuffer being used to represent the bytes behind a Blob.
This also allows us to use a stronger type for a function that needs
to return a Blob URL entry's object.
A couple of reasons:
- Origin's Host (when in the tuple state) can't be null
- There's an "empty host" concept in the spec which is NOT the same as a
null Host, and that was confusing me.
