We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
There will be a lot of different cases where we'll return an error
response, and having a customized Promise rejection message seems quite
useful.
Note that this has to be distinct from the existing 'status message',
which is required to be empty in those cases.
This is the way.
On a more serious note, there's no reason to keep adding ref-counted
classes to LibWeb now that the majority of classes is GC'd - it only
adds the risk of discovering some cycle down the line, and forces us to
use handles as we can't visit().
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!
This is needed to eventually share a header list between a Request or
Response object's internal infra request/response and the object's
exposed Header object.
A Request/Response instance should always be heap-allocated and have
clear ownership, so let's also wrap it in a NonnullOwnPtr instead of
putting them on the stack.
The Fetch spec unfortunately will cause a name clash between the Request
concept and the Request JS object - both cannot live in the Web::Fetch
namespace, and WrapperGenerator generally assumes `Web::<Name>` for
things living in the `<Name>/` subdirectory, so let's instead move infra
code into its own namespace - it already sits in a (sub-)subdirectory
anyway.
