Add userName and userDisplayName to webdriver

This PR adds the userName and userDisplayName properties to the
webdriver's credential parameters. These properties are useful to test
the new signalCurrentUserDetails method, both on WPTs and for web
developers.

Closes #2143

index.bs

@@ -8013,6 +8013,22 @@ The <dfn>Credential Parameters</dfn> is a JSON [=Object=] passed to the [=remote
                 </td>
                 <td>boolean</td>
             </tr>
+            <tr>
+                <td>|userName|</td>
+                <td>
+                    The {{PublicKeyCredentialUserEntity|user}}'s {{PublicKeyCredentialEntity/name}} associated to the credential.
+                    If unset, the value will default to the empty string.
+                </td>
+                <td>string</td>
+            </tr>
+            <tr>
+                <td>|userDisplayName|</td>
+                <td>
+                    The {{PublicKeyCredentialUserEntity|user}}'s {{PublicKeyCredentialUserEntity/displayName}} associated to the credential.
+                    If unset, the value will default to the empty string.
+                </td>
+                <td>string</td>
+            </tr>
         </tbody>
     </table>
 </figure>
@@ -8053,6 +8069,10 @@ The [=remote end steps=] are:
  1. If |backupEligibility| is not defined, set |backupEligibility| to the value of the |authenticator|'s |defaultBackupEligibility|.
  1. Let |backupState| be the |parameters|' |backupState| property.
  1. If |backupState| is not defined, set |backupState| to the value of the |authenticator|'s |defaultBackupState|.
+ 1. Let |userName| be the |parameters|' |userName| property.
+ 1. If |userName| is not defined, set |userName| to the empty string.
+ 1. Let |userDisplayName| be the |parameters|' |userDisplayName| property.
+ 1. If |userDisplayName| is not defined, set |userDisplayName| to the empty string.
  1. Let |credential| be a new [=Client-side discoverable Public Key Credential Source=] if |isResidentCredential| is [TRUE]
      or a [=Server-side Public Key Credential Source=] otherwise whose items are:
     : [=public key credential source/type=]
@@ -8065,6 +8085,8 @@ The [=remote end steps=] are:
     :: |rpId|
     : [=public key credential source/userHandle=]
     :: |userHandle|
+    : [=public key credential source/otherUI=]
+    :: Construct from |userName| and |userDisplayName|.
  1. Set the |credential|'s [=backup eligibility=] [=credential property=] to |backupEligibility|.
  1. Set the |credential|'s [=backup state=] [=credential property=] to |backupState|.
  1. Associate a [=signature counter=] |counter| to the |credential| with a starting value equal to the |parameters|'