Fix contradictory missing value default for formmethod=""

Closes #5804, by stating the defaults for method="" and formmethod=""
individually. Also ports this structure to the nearby enctype="" and
formenctype="" pair, which did not have a contradiction, but were
sacrificing clarity for brevity.

source

@@ -52667,13 +52667,13 @@ form.method === input; // => true</code></pre>
 
   </ul>
 
-  <p>The <i data-x="invalid value default">invalid value default</i> for these attributes is the <span
-  data-x="attr-fs-method-GET">GET</span> state. The <i data-x="missing value default">missing value default</i> for the <code
-  data-x="attr-fs-method">method</code> attribute is also the <span
-  data-x="attr-fs-method-GET">GET</span> state. (There is no <i
-  data-x="missing value default">missing value default</i> or <i
-  data-x="invalid value default">invalid value default</i> for the
-  <code data-x="attr-fs-formmethod">formmethod</code> attribute.)</p>
+  <p>The <code data-x="attr-fs-method">method</code> attribute's <i data-x="invalid value
+  default">invalid value default</i> and <i data-x="missing value default">missing value default</i>
+  are both the <span data-x="attr-fs-method-GET">GET</span> state.</p>
+
+  <p>The <code data-x="attr-fs-formmethod">formmethod</code> attribute's <i data-x="invalid value
+  default">invalid value default</i> is the <span data-x="attr-fs-method-GET">GET</span> state. It
+  has no <i data-x="missing value default">missing value default</i>.</p>
 
   <p>The <dfn data-x="concept-fs-method">method</dfn> of an element is one of those states. If the
   element is a <span data-x="concept-submit-button">submit button</span> and has a <code
@@ -52747,11 +52747,15 @@ form.method === input; // => true</code></pre>
    <li>The "<dfn><code data-x="attr-fs-enctype-text">text/plain</code></dfn>" keyword and corresponding state.</li>
   </ul>
 
-  <p>The <i data-x="invalid value default">invalid value default</i> for these attributes is the <code
-  data-x="attr-fs-enctype-urlencoded">application/x-www-form-urlencoded</code> state. The <i data-x="missing value default">missing value default</i> for the <code data-x="attr-fs-enctype">enctype</code> attribute is also the <code
-  data-x="attr-fs-enctype-urlencoded">application/x-www-form-urlencoded</code> state. (There is no
-  <i data-x="missing value default">missing value default</i> for the <code
-  data-x="attr-fs-formenctype">formenctype</code> attribute.)</p>
+  <p>The <code data-x="attr-fs-enctype">enctype</code> attribute's <i data-x="invalid value
+  default">invalid value default</i> and <i data-x="missing value default">missing value default</i>
+  are both the <code data-x="attr-fs-enctype-urlencoded">application/x-www-form-urlencoded</code>
+  state.</p>
+
+  <p>The <code data-x="attr-fs-formenctype">formenctype</code> attribute's <i data-x="invalid value
+  default">invalid value default</i> is the <code
+  data-x="attr-fs-enctype-urlencoded">application/x-www-form-urlencoded</code> state. It has no <i
+  data-x="missing value default">missing value default</i>.</p>
 
   <p>The <dfn data-x="concept-fs-enctype">enctype</dfn> of an element is one of those three states.
   If the element is a <span data-x="concept-submit-button">submit button</span> and has a <code