Add activation token parameter to Email portal

This may be needed by the email client to function properly

data/org.freedesktop.impl.portal.Email.xml

@@ -81,6 +81,12 @@
               The uris for files to attach.
             </para></listitem>
           </varlistentry>
+          <varlistentry>
+            <term>activation_token s</term>
+            <listitem><para>
+              A token that can be used to activate the chosen application.
+            </para></listitem>
+          </varlistentry>
         </variablelist>
     -->
     <method name="ComposeEmail">

data/org.freedesktop.portal.Email.xml

@@ -26,7 +26,7 @@
       This simple portal lets sandboxed applications request to send an email,
       optionally providing an address, subject, body and attachments.
 
-      This documentation describes version 3 of this interface.
+      This documentation describes version 4 of this interface.
   -->
   <interface name="org.freedesktop.portal.Email">
     <!--
@@ -109,6 +109,14 @@
               File descriptors for files to attach.
             </para></listitem>
           </varlistentry>
+          <varlistentry>
+            <term>activation_token s</term>
+            <listitem><para>
+              A token that can be used to activate the chosen application.
+            </para><para>
+              The activation_token option was introduced in version 4 of the interface.
+            </para></listitem>
+          </varlistentry>
         </variablelist>
 
         All the keys in the options are are optional.

src/email.c

@@ -192,7 +192,8 @@ static XdpOptionKey compose_email_options[] = {
   { "cc", G_VARIANT_TYPE_STRING_ARRAY, validate_email_addresses },
   { "bcc", G_VARIANT_TYPE_STRING_ARRAY, validate_email_addresses },
   { "subject", G_VARIANT_TYPE_STRING, validate_email_subject },
-  { "body", G_VARIANT_TYPE_STRING, NULL }
+  { "body", G_VARIANT_TYPE_STRING, NULL },
+  { "activation_token", G_VARIANT_TYPE_STRING, NULL }
 };
 
 static gboolean