Pass better ancestor/root information to (re)moving steps

For removing steps and moving steps, instead of passing only oldParent (which is null when the removed node is not the root of the removed subtree), pass both isSubtreeRoot and oldAncestor (renamed from oldParent because it's not always a parent now).

This is the DOM spec part of the fix for whatwg/html#12098.

Author: dbaron

dom.bs

@@ -2994,8 +2994,9 @@ null.
 <div algorithm>
 <p><a lt="Other applicable specifications">Specifications</a> may define
 <dfn export id=concept-node-move-ext>moving steps</dfn> for all or some <a for=/>nodes</a>. The
-algorithm is passed a <a for=/>node</a> <var>movedNode</var>, and a <a for=/>node</a>-or-null
-<var ignore>oldParent</var> as indicated in the <a for=/>move</a> algorithm below. Like the
+algorithm is passed a <a for=/>node</a> <var>movedNode</var>, a boolean
+<var ignore>isSubtreeRoot</var>, and a <a for=/>node</a> <var ignore>oldAncestor</var>
+as indicated in the <a for=/>move</a> algorithm below. Like the
 <a>insertion steps</a>, these steps must not modify the <a>node tree</a> that
 <var>movedNode</var> <a>participates</a> in, create <a for=/>browsing contexts</a>,
 <a lt="fire an event">fire events</a>, or otherwise execute JavaScript. These steps may queue tasks
@@ -3107,14 +3108,16 @@ to do these things asynchronously, however.
   <var>node</var>, in <a>shadow-including tree order</a>:
 
   <ol>
+   <li><p>Let <var>isSubtreeRoot</var> be true if <var>inclusiveDescendant</var> is
+   <var>node</var>; otherwise false.
+
    <li>
-    <p>If <var>inclusiveDescendant</var> is <var>node</var>, then run the <a>moving steps</a> with
-    <var>inclusiveDescendant</var> and <var>oldParent</var>. Otherwise, run the <a>moving steps</a>
-    with <var>inclusiveDescendant</var> and null.
+    <p>Run the <a>moving steps</a> with <var>inclusiveDescendant</var>, <var>isSubtreeRoot</var>,
+    and <var>oldParent</var>.
 
     <p class="note">Because the <a>move</a> algorithm is a separate primitive from
-    <a for=/>insert</a> and <a for=/>remove</a>, it does not invoke the traditional
-    <a>insertion steps</a> or <a>removing steps</a> for <var>inclusiveDescendant</var>.
+    <a for=/>insert</a> and <a for=/>remove</a>, it does not invoke the <a>insertion steps</a>
+    or <a>removing steps</a> for <var>inclusiveDescendant</var>.
    </li>
 
    <li><p>If <var>inclusiveDescendant</var> is <a for=Element>custom</a> and <var>newParent</var> is
@@ -3270,9 +3273,9 @@ from a <a for=/>node</a> <var>parent</var>:
 <div algorithm>
 <p><a lt="Other applicable specifications">Specifications</a> may define
 <dfn export id=concept-node-remove-ext>removing steps</dfn> for all or some <a for=/>nodes</a>. The
-algorithm is passed a <a for=/>node</a> <var ignore>removedNode</var> and a
-<a for=/>node</a>-or-null <var ignore>oldParent</var>, as indicated in the <a for=/>remove</a>
-algorithm below.
+algorithm is passed a <a for=/>node</a> <var ignore>removedNode</var>, a boolean
+<var ignore>isSubtreeRoot</var>, and a <a for=/>node</a> <var ignore>oldAncestor</var> as indicated
+in the <a for=/>remove</a> algorithm below.
 </div>
 
 <div algorithm=remove>
@@ -3313,7 +3316,7 @@ optional boolean <dfn for=remove><var>suppressObservers</var></dfn> (default fal
    <li><p>Run <a>assign slottables for a tree</a> with <var>node</var>.
   </ol>
 
- <li><p>Run the <a>removing steps</a> with <var>node</var> and <var>parent</var>.
+ <li><p>Run the <a>removing steps</a> with <var>node</var>, true, and <var>parent</var>.
 
  <li><p>Let <var>isParentConnected</var> be <var>parent</var>'s <a>connected</a>.
 
@@ -3330,7 +3333,7 @@ optional boolean <dfn for=remove><var>suppressObservers</var></dfn> (default fal
   <a>shadow-including tree order</a>:
 
   <ol>
-   <li><p>Run the <a>removing steps</a> with <var>descendant</var> and null.
+   <li><p>Run the <a>removing steps</a> with <var>descendant</var>, false, and <var>parent</var>.
 
    <li><p>If <var>descendant</var> is <a for=Element>custom</a> and <var>isParentConnected</var>
    is true, then <a>enqueue a custom element callback reaction</a> with <var>descendant</var>,