ensure response body is utf-8 encoded (#1404)

As currently worded, the response's value may be double
JSON-encoded, which is far from ideal. We also fail to
state that the bytes must be UTF-8 encoded.

Author: shs96c

index.html

@@ -582,9 +582,10 @@ <h3>Processing model</h3>
    <dd>"<code>no-cache</code>"
   </dl>
 
- <li><p>Let <var>response</var>’s <a>body</a> be a JSON <a>Object</a>
-  with a key "<code>value</code>"
-  set to the <a>JSON serialization</a> of <var>data</var>.
+ <li><p>Let <var>response</var>’s <a>body</a> be
+  the <a data-lt="utf-8 encode">UTF-8 encoded</a> <a>JSON
+  serialization</a> of a JSON <a>Object</a> with a key
+  "<code>value</code>" set to <var>data</var>.
 
  <li><p>Let <var>response bytes</var> be the byte sequence resulting
   from serializing <var>response</var> according to the rules in [[!RFC7230]].
@@ -9359,6 +9360,12 @@ <h2>Index</h2>
    <!-- undefined --> <li><dfn><a href=https://www.ecma-international.org/ecma-262/5.1/#sec-4.3.9>Undefined</a></dfn>
   </ul>
 
+ <dt>Encoding
+ <dd><p>The following terms are defined in the WHATWG Encoding specification: [[!ENCODING]]
+  <ul>
+   <!-- UTF-8 Encode --> <li><dfn><a href="https://encoding.spec.whatwg.org/#utf-8-encode">UTF-8 Encode</a></dfn>
+  </ul>
+
  <dt>Fetch
  <dd><p>The following terms are defined in the WHATWG Fetch specification: [[!FETCH]]
   <ul>