Do not throw when cloning %ObjectPrototype%

This matches the majority of existing implementations. The spec said it
should throw, but this was arguably accidental fallout from some
refactoring of the JavaScript specification.

Closes #5158.

Author: domenic

source

@@ -2934,6 +2934,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
      <li><dfn data-x-href="https://tc39.es/ecma262/#running-execution-context">running JavaScript execution context</dfn></li>
      <li><dfn data-x-href="https://tc39.es/ecma262/#surrounding-agent">surrounding agent</dfn></li>
      <li><dfn data-x-href="https://tc39.es/ecma262/#sec-abstract-closure">abstract closure</dfn></li>
+     <li><dfn data-x-href="https://tc39.es/ecma262/#immutable-prototype-exotic-object">immutable prototype exotic object</dfn></li>
      <li><dfn data-x-href="https://tc39.es/ecma262/#sec-well-known-symbols">Well-Known Symbols</dfn>, including
          <dfn>@@hasInstance</dfn>,
          <dfn>@@isConcatSpreadable</dfn>,
@@ -2945,6 +2946,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
          <dfn>%EvalErrorPrototype%</dfn>,
          <dfn data-x-href="https://tc39.es/ecma262/#sec-properties-of-the-function-prototype-object">%FunctionPrototype%</dfn>,
          <dfn data-x-href="https://tc39.es/ecma262/#sec-json.parse">%JSONParse%</dfn>,
+         <dfn data-x-href="https://tc39.es/ecma262/#sec-properties-of-the-object-prototype-object">%ObjectPrototype%</dfn>,
          <dfn data-x-href="https://tc39.es/ecma262/#sec-object.prototype.valueof">%ObjProto_valueOf%</dfn>,
          <dfn>%RangeErrorPrototype%</dfn>,
          <dfn>%ReferenceErrorPrototype%</dfn>,
@@ -8446,8 +8448,10 @@ interface <dfn>DOMStringList</dfn> {
    </li>
 
    <li>
-    <p>Otherwise, if <var>value</var> is an exotic object, then throw a
-    <span>"<code>DataCloneError</code>"</span> <code>DOMException</code>.</p>
+    <p>Otherwise, if <var>value</var> is an exotic object and <var>value</var> is not the
+    <span>%ObjectPrototype%</span> intrinsic object associated with any <span>JavaScript
+    realm</span>, then throw a <span>"<code>DataCloneError</code>"</span>
+    <code>DOMException</code>.</p>
 
     <p class="example">For instance, a proxy object.</p>
    </li>
@@ -8461,6 +8465,10 @@ interface <dfn>DOMStringList</dfn> {
 
      <li><p>Set <var>deep</var> to true.</p></li>
     </ol>
+
+    <p class="note"><span>%ObjectPrototype%</span> will end up being handled via this step and
+    subsequent steps. The end result is that its exoticness is ignored, and after deserialization
+    the result will be an empty object (not an <span>immutable prototype exotic object</span>).
    </li>
 
    <li><p><span data-x="map set">Set</span> <var>memory</var>[<var>value</var>] to