LibWeb: Move strip_and_collapse_whitespace() to Infra/

...and make it spec compliant by considering all ASCII whitespace,
greatly simplifying it in the process :^)

Userland/Libraries/LibWeb/Infra/Strings.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+
+namespace Web::Infra {
+
+String strip_and_collapse_whitespace(StringView string);
+
+}