LibWeb: Implement spec-compliant MIME type struct and parser

This will be used by XHR to extract the Content-Type MIME type to
retrieve the charset.

Userland/Libraries/LibWeb/Fetch/AbstractOperations.h

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+
+namespace Web::Fetch {
+
+enum class HttpQuotedStringExtractValue {
+    No,
+    Yes,
+};
+
+String collect_an_http_quoted_string(GenericLexer& lexer, HttpQuotedStringExtractValue extract_value);
+
+}