We need to keep an Infrastructure::Request::BodyType around as we're not
sure what's actually inside, instead accessing Infrastructure::Body
directly.
Co-authored-by: Luke Wilde <lukew@serenityos.org>
With the addition of the 'fetch params' struct, the single ownership
model we had so far falls apart completely.
Additionally, this works nicely for FilteredResponse's internal response
instead of risking a dangling reference.
Replacing the public constructor with a create() function also found a
few instances of a Request being stack-allocated!
