Report all hostname state failures for URLPattern

URLPattern's canonicalize a hostname is the only invocation of the basic URL parser with a URL and state override set to hostname state that looks at the return failure.

And since the URL that URLPattern uses is a dummy URL that is ideally not exposed, knowing about all the failure conditions is kind of important.

(Now technically the second return failure added here cannot be observed as the dummy URL won't have credentials or a non-null port, but it seemed good to change that at the same time for consistency.)

This is covered by existing URLPattern web-platform-tests. Some more background can be found in whatwg/urlpattern#252.

Author: annevk

url.bs

@@ -2538,15 +2538,16 @@ and then runs these steps:
      <a>file host state</a>.
 
      <li>
-      <p>Otherwise, if <a>c</a> is U+003A (:) and <var>insideBrackets</var> is false, then:
+      <p>Otherwise, if <a>c</a> is U+003A (:) and <var>insideBrackets</var> is false:
 
       <ol>
        <li><p>If <var>buffer</var> is the empty string, <a>host-missing</a> <a>validation error</a>,
        return failure.
        <!-- No URLs with port, but without host. -->
 
        <li><p>If <var>state override</var> is given and <var>state override</var> is
-       <a>hostname state</a>, then return.
+       <a>hostname state</a>, then return failure.
+       <!-- API validation error -->
 
        <li><p>Let <var>host</var> be the result of <a>host parsing</a> <var>buffer</var> with
        <var>url</var> <a>is not special</a>.
@@ -2566,7 +2567,7 @@ and then runs these steps:
        <li><p><var>url</var> <a>is special</a> and <a>c</a> is U+005C (\)
       </ul>
 
-      <p>then decrease <var>pointer</var> by 1, and then:
+      <p>then decrease <var>pointer</var> by 1, and:
 
       <ol>
        <li><p>If <var>url</var> <a>is special</a> and <var>buffer</var> is the empty string,
@@ -2576,7 +2577,7 @@ and then runs these steps:
 
        <li><p>Otherwise, if <var>state override</var> is given, <var>buffer</var> is the empty
        string, and either <var>url</var> <a>includes credentials</a> or <var>url</var>'s
-       <a for=url>port</a> is non-null, return.
+       <a for=url>port</a> is non-null, then return failure.
        <!-- API validation error -->
 
        <li><p>Let <var>host</var> be the result of <a>host parsing</a> <var>buffer</var> with