LibWeb: Move extract_body() into Fetch

Author: https://github.com/linusg
Commit: 571f4e3ebb
Pull-request: https://github.com/SerenityOS/serenity/pull/15323
Reviewed-by: https://github.com/davidot ✅
Reviewed-by: https://github.com/kennethmyhra ✅

Userland/Libraries/LibWeb/Forward.h

@@ -189,6 +189,7 @@ class HeadersIterator;
 
 namespace Web::Fetch::Infrastructure {
 class Body;
+struct BodyWithType;
 struct Header;
 class HeaderList;
 class Request;