Stop using “strictly split” in “validate and extract”

This change causes the “validate and extract” algorithm to stop calling “strictly split” and instead split on the first colon only. Given the qualified name “foo:bar:baz”, that produces the local name “bar:baz”.

Otherwise, without this change, using “strictly split” produces the prefix “foo” and local name “bar" — discarding the “:baz” part.

Tests: web-platform-tests/wpt#58331.

Additional context: WICG/sanitizer-api#373. Fixes #1453.

Author: sideshowbarker

dom.bs

@@ -254,12 +254,9 @@ U+0000 NULL, or U+003E (>).
   <p>If <var>qualifiedName</var> contains a U+003A (:):
 
   <ol>
-   <li><p>Let <var>splitResult</var> be the result of running <a>strictly split</a> given
-   <var>qualifiedName</var> and U+003A (:).
+   <li><p>Set <var>prefix</var> to the part of <var>qualifiedName</var> before the first U+003A (:).
 
-   <li><p>Set <var>prefix</var> to <var>splitResult</var>[0].
-
-   <li><p>Set <var>localName</var> to <var>splitResult</var>[1].
+   <li><p>Set <var>localName</var> to the part of <var>qualifiedName</var> after the first U+003A (:).
 
    <li><p>If <var>prefix</var> is not a [=valid namespace prefix=], then [=throw=] an
    "{{InvalidCharacterError}}" {{DOMException}}.