Switch to <em> where appropriate

Author: rbuckton

spec.html

@@ -49780,9 +49780,9 @@ <h1>Resource Management</h1>
       <h1>Common Resource Management Interfaces</h1>
 
       <emu-clause id="sec-disposable-interface">
-        <h1>The <i>Disposable</i> Interface</h1>
-        <p>The <i>Disposable</i> interface includes the property described in <emu-xref href="#table-disposable-interface-required-properties"></emu-xref>:</p>
-        <emu-table id="table-disposable-interface-required-properties" caption="<i>Disposable</i> Interface Required Properties">
+        <h1>The <em>Disposable</em> Interface</h1>
+        <p>The <em>Disposable</em> interface includes the property described in <emu-xref href="#table-disposable-interface-required-properties"></emu-xref>:</p>
+        <emu-table id="table-disposable-interface-required-properties" caption="<em>Disposable</em> Interface Required Properties">
           <table>
             <tr>
               <th>