LibWeb: Make Fetch::Infrastructure::{Request,Response,HeaderList} GC'd

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().

Userland/Libraries/LibWeb/Fetch/Infrastructure/HTTP/Headers.cpp

@@ -11,6 +11,8 @@
 #include <AK/GenericLexer.h>
 #include <AK/QuickSort.h>
 #include <AK/ScopeGuard.h>
+#include <LibJS/Heap/Heap.h>
+#include <LibJS/Runtime/VM.h>
 #include <LibRegex/Regex.h>
 #include <LibWeb/Fetch/Infrastructure/HTTP.h>
 #include <LibWeb/Fetch/Infrastructure/HTTP/Headers.h>
@@ -42,6 +44,11 @@ ErrorOr<Header> Header::from_string_pair(StringView name, StringView value)
     };
 }
 
+JS::NonnullGCPtr<HeaderList> HeaderList::create(JS::VM& vm)
+{
+    return { *vm.heap().allocate_without_realm<HeaderList>() };
+}
+
 // https://fetch.spec.whatwg.org/#header-list-contains
 bool HeaderList::contains(ReadonlyBytes name) const
 {