LibWeb: Add definitions from '2.2.4. Bodies' in the Fetch spec

...at least the ones that don't require an implementation of the Streams
spec :^)

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

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Fetch/Infrastructure/HTTP/Bodies.h>
+
+namespace Web::Fetch {
+
+Body::Body(ReadableStreamDummy stream)
+    : m_stream(stream)
+{
+}
+
+Body::Body(ReadableStreamDummy stream, SourceType source, Optional<u64> length)
+    : m_stream(stream)
+    , m_source(move(source))
+    , m_length(move(length))
+{
+}
+
+}