libbnetservices: BUrlResult is no longer a BArchivable

The switch to make BUrlResult serializable was debuted in
f9e1854f198d4200f21a9cbe29fdfb0fabbe192f with the rationale is that
BHttpRequest auto-redirection might cause the headers to become
obsolete by the time a client process the BMessage received from
BUrlProtocolDispatchingListener.

With the change to BHttpRequest to not notify listeners when
auto-redirection is enabled, this is no longer the case and the
serialization code can go away now. This simplifies BUrlResult and its
subclasses, and gain us some performance for clients using
BUrlProtocolDispatchingListener as the result object no longer has to be
serialized.

This also change the ABI of BUrlProtocolListener::HeadersReceived to no
longer passing a BUrlResult.

Additionally, BUrlResult and BHttpResult now express the size of the content
as an off_t, thus allowing results larger than 4 GB.

Change-Id: I9dd29a8b26fdd9aa8e5bbad8d1728084f136312d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3082
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

libnetservices.a: Put the experimental API into BPrivate::Network namespace

In order to prevent classes between libnetapi.so with the legacy API and
applications using the libnetservices.a library, the latter will have the
classes in a distinct namespace.

In the implementation, both libbnetapi.so and libnetservices.a will use the
same header and source files. If LIBNETAPI_DEPRECATED is defined during build,
the headers and source will have binary compatible behavior. Otherwise, the
classes and other objects will be put in the HaikuExt namespace.

In order to build the libbnetapi.so and libnetservices.a with the proper
build configuration, there is a stub `src/kits/net/libnetapi_deprecated` folder
that applies the special configuration to the source files.

Currently HaikuDepot, Webpositive, libshared.a and the http_streamer add on
use the compatible API in libbnetapi.so.

Change-Id: Ic73e9f271ef75749adda46f6f72e9a0b2851b461
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3667
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

libnetapi.so: move deprecated classes out into a libnetservices directory

These classes have been moved to the public API too soon, and they need some
more time to mature before they can be declared stable.

In this first step the classes that are involved, are moved to a separate
folder. They will still be linked to libnetapi.so, so that binaries that
depend on them currently will not break.

Change-Id: I6c16f17573d819314a27936f065ebe675846f763
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3664
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>