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.cpp

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/String.h>
+#include <AK/Utf8View.h>
+#include <LibWeb/Infra/CharacterTypes.h>
+#include <LibWeb/Infra/Strings.h>
+
+namespace Web::Infra {
+
+// https://infra.spec.whatwg.org/#strip-and-collapse-ascii-whitespace
+String strip_and_collapse_whitespace(StringView string)
+{
+    // Replace any sequence of one or more consecutive code points that are ASCII whitespace in the string with a single U+0020 SPACE code point.
+    StringBuilder builder;
+    for (auto code_point : Utf8View { string }) {
+        if (Infra::is_ascii_whitespace(code_point)) {
+            if (!builder.string_view().ends_with(' '))
+                builder.append(' ');
+            continue;
+        }
+        builder.append_code_point(code_point);
+    }
+
+    // ...and then remove any leading and trailing ASCII whitespace from that string.
+    return builder.string_view().trim(Infra::ASCII_WHITESPACE);
+}
+
+}