Fix attribute annotation code for FACEs

[domenic]

The root issue fixed here is that the domintro for custom elements was not properly listing the attribute explanation for readonly.

This fixes several related issues:

• <span>form-associated custom elements</span> was not matching the
  regex that was looking for <code> in the attribute index.
• Changing the regex to look for span or code causes many other lines to
  be picked up. Thus, we introduce the new 'tr' state into the state
  machine to better detect the first line of a <tr>.
• Even with that, we were now dying on global attributes, since they
  don't have a domintro to get substituted in to. So we remove that
  error state.
• Finally, we were now substituting in even in cases that just mention
  the attribute, like "Global attributes, except the is attribute". So,
  we need to add an escape hatch for that.

---

I've tested that this produces the following diff on the full spec:

@@ -22284,7 +22284,7 @@ wormhole connection.&lt;/mark>&lt;/p></code></pre>
    <dd><span>Phrasing content</span>.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
    <dd><span>Global attributes</span></dd>
-   <dd>Also, the <code data-x="attr-dir">dir</code> global attribute has special semantics on this element.</dd>
+   <dd>Also, the <code data-x="attr-dir">dir</code> global attribute has special semantics on this element: <span data-x="the directionality">The text directionality</span> of the element.</dd>
    <dt><span data-x="concept-element-dom">DOM interface</span>:</dt>
    <dd>Uses <code>HTMLElement</code>.</dd>
   </dl>
@@ -22345,7 +22345,7 @@ wormhole connection.&lt;/mark>&lt;/p></code></pre>
    <dd><span>Phrasing content</span>.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
    <dd><span>Global attributes</span></dd>
-   <dd>Also, the <code data-x="attr-dir">dir</code> global attribute has special semantics on this element.</dd>
+   <dd>Also, the <code data-x="attr-dir">dir</code> global attribute has special semantics on this element: <span data-x="the directionality">The text directionality</span> of the element.</dd>
    <dt><span data-x="concept-element-dom">DOM interface</span>:</dt>
    <dd>Uses <code>HTMLElement</code>.</dd>
   </dl>
@@ -66865,10 +66865,10 @@ document.body.append(parent);
    <dt><span data-x="concept-element-content-model">Content model</span>:</dt>
    <dd><span>Transparent</span>.</dd>
    <dt><span data-x="concept-element-attributes">Content attributes</span>:</dt>
-   <dd><span>Global attributes</span>, except the <code data-x="attr-is">is</code> attribute</dd>
+   <dd><span>Global attributes</span>, except the <code data-x="attr-is">is</code> attribute<!-- no-annotate --></dd>
    <dd><code data-x="attr-fae-form">form</code>, for <span data-x="form-associated custom element">form-associated custom elements</span> &mdash; Associates the element with a <code>form</code> element</dd>
    <dd><code data-x="attr-fe-disabled">disabled</code>, for <span data-x="form-associated custom element">form-associated custom elements</span> &mdash; Whether the form control is disabled</dd>
-   <dd><code data-x="attr-face-readonly">readonly</code>, for <span data-x="form-associated custom element">form-associated custom elements</span></dd>
+   <dd><code data-x="attr-face-readonly">readonly</code>, for <span data-x="form-associated custom element">form-associated custom elements</span> &mdash; Affects <code data-x="dom-ElementInternals-willValidate">willValidate</code></dd>
    <dd><code data-x="attr-fe-name">name</code>, for <span data-x="form-associated custom element">form-associated custom elements</span> &mdash; Name of the element to use for <span>form submission</span> and in the <code data-x="dom-form-elements">form.elements</code> API </dd>
    <dd>Any other attribute that has no namespace (see prose).</dd>
    <dt><span data-x="concept-element-dom">DOM interface</span>:</dt>

For dir, we can either add <!-- no-annotate -->, or we can add actually special definitions for bdi and bdo.

[annevk]

Mike should probably review the Perl, but this sounds good to me.

[sideshowbarker]

Thanks for doing this