This currently uses a non spec-compliant property on the Response
object, which represents the time that the Response was created.
Setting this value allows `Performance.timeOrigin` to return a
reasonable value.
The spec for filtered responses states:
Unless stated otherwise a filtered response’s associated concepts
(such as its body) refer to the associated concepts of its internal
response.
This includes setting its associated concepts. In particular, when the
filtered response's body is set upon fetching a request with integrity
metadata, we must set the internal response's body instead.
Further restrictions that apply to filtered response subclasses (such as
opaque filtered responses having a status code of 0) are already
implemented.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
