Fix definition of site for null-registrable-domain cases

In particular, different ports on the same IP address need to be
considered same-site, and public-suffix roots need to be considered
same-site to their subdomains.

Closes #5940; see
#5940 (comment) in
particular.

source

@@ -80073,9 +80073,7 @@ interface <dfn>BarProp</dfn> {
   <p>A <dfn export>scheme-and-registrable-domain</dfn> is a <span>tuple</span> of a <span
   data-x="concept-url-scheme">scheme</span> and a <span data-x="concept-domain">domain</span>.</p>
 
-  <p>A <dfn export>site</dfn> is an <span data-x="concept-origin-opaque">opaque origin</span>, a
-  <span data-x="concept-origin-tuple">tuple origin</span> whose <span
-  data-x="concept-origin-host">host</span>'s <span>registrable domain</span> is null, or a
+  <p>A <dfn export>site</dfn> is an <span data-x="concept-origin-opaque">opaque origin</span> or a
   <span>scheme-and-registrable-domain</span>.</p>
 
   <p>To <dfn export>obtain a site</dfn>, given an origin <var>origin</var>, run these steps:</p>
@@ -80085,7 +80083,8 @@ interface <dfn>BarProp</dfn> {
    return <var>origin</var>.</p></li>
 
    <li><p>If <var>origin</var>'s <span data-x="concept-origin-host">host</span>'s <span>registrable
-   domain</span> is null, then return <var>origin</var>.</p></li>
+   domain</span> is null, then return <span data-x="concept-origin-scheme">scheme</span>,
+   <var>origin</var>'s <span data-x="concept-origin-host">host</span>).</p></li>
 
    <li><p>Return (<var>origin</var>'s <span data-x="concept-origin-scheme">scheme</span>,
    <var>origin</var>'s <span data-x="concept-origin-host">host</span>'s <span>registrable