Set the Realm when compiling event handler IDL attributes

Fixes #1956. Also changes the error reporting global used to be more straightforward.

source

@@ -88585,9 +88585,8 @@ typedef <span>OnBeforeUnloadEventHandlerNonNull</span>? <dfn>OnBeforeUnloadEvent
      <span>form owner</span>, let <var>form owner</var> be that <span>form owner</span>.
      Otherwise, let <var>form owner</var> be null.</p></li>
 
-     <li><p>Let <var>script settings</var> be the <span>relevant settings object</span> of
-     <var>document</var>'s <span data-x="concept-document-bc">browsing context</span>'s
-     <code>Window</code> object.</p></li>
+     <li><p>Let <var>settings object</var> be the <span>relevant settings object</span> of
+     <var>document</var>.</p></li>
 
      <li>
 
@@ -88600,10 +88599,10 @@ typedef <span>OnBeforeUnloadEventHandlerNonNull</span>? <dfn>OnBeforeUnloadEvent
 
        <li><p><span>Report the error</span> for the appropriate <span
        data-x="concept-script">script</span> and with the appropriate position (line number and
-       column number) given by <var>location</var>, using the <span
-       data-x="concept-settings-object-global">global object</span> specified by <var>script
-       settings</var> as the target. If the error is still <i data-x="concept-error-nothandled">not
-       handled</i> after this, then the error may be reported to a developer console.</p></li>
+       column number) given by <var>location</var>, using <var>settings object</var>'s <span
+       data-x="concept-settings-object-global">global object</span>. If the error is still <i
+       data-x="concept-error-nothandled">not handled</i> after this, then the error may be reported
+       to a developer console.</p></li>
 
        <li><p>Return null.</p></li>
 
@@ -88620,6 +88619,10 @@ typedef <span>OnBeforeUnloadEventHandlerNonNull</span>? <dfn>OnBeforeUnloadEvent
 
      </li>
 
+     <li><p>Push <var>settings object</var>'s <span>realm execution context</span> onto the
+     <span>JavaScript execution context stack</span>; it is now the <span>running JavaScript
+     execution context</span>.</p></li>
+
      <li>
 
       <p>Let <var>function</var> be the result of calling <span
@@ -88694,6 +88697,9 @@ typedef <span>OnBeforeUnloadEventHandlerNonNull</span>? <dfn>OnBeforeUnloadEvent
 
      </li>
 
+     <li><p>Remove <var>settings object</var>'s <span>realm execution context</span> from the
+     <span>JavaScript execution context stack</span>.</p></li>
+
      <!-- SCRIPT EXEC, sorta -->
      <li><p>Set <var>H</var>'s value to <var>function</var>.</p></li>