Add "webidentity" destination for FedCM

CSP PR: w3c/webappsec-csp#567.

Tests: web-platform-tests/wpt#36230.

fetch.bs

@@ -1517,6 +1517,7 @@ the empty string,
 "<code>style</code>",
 "<code>track</code>",
 "<code>video</code>",
+"<code>webidentity</code>",
 "<code>worker</code>", or
 "<code>xslt</code>". Unless stated otherwise it is the empty string.
 
@@ -1548,7 +1549,7 @@ not always relevant and might require different behavior.
    <th>CSP directive
    <th>Features
   <tr>
-   <td rowspan=19>""
+   <td rowspan=20>""
    <td>"<code>report</code>"
    <td rowspan=2>&mdash;
    <td>CSP, NEL reports.
@@ -1611,6 +1612,10 @@ not always relevant and might require different behavior.
    <td>"<code>sharedworker</code>"
    <td><code>child-src</code>, <code>script-src</code>, <code>worker-src</code>
    <td><code>SharedWorker</code>
+  <tr>
+   <td>"<code>webidentity</code>"
+   <td><code>connect-src</code>
+   <td><code>Federated Credential Management requests</code>
   <tr>
    <td>"<code>worker</code>"
    <td><code>child-src</code>, <code>script-src</code>, <code>worker-src</code>