calendar-management: Port credentials dialog to AdwToolbarView and AdwWindow

src/gui/calendar-management/gcal-new-calendar-page.c

@@ -51,7 +51,7 @@ struct _GcalNewCalendarPage
   GtkWidget          *cancel_button;
   GtkWidget          *credentials_cancel_button;
   GtkWidget          *credentials_connect_button;
-  GtkWindow          *credentials_dialog;
+  AdwWindow          *credentials_dialog;
   GtkEntry           *credentials_password_entry;
   GtkEntry           *credentials_user_entry;
   GtkColorDialogButton *local_calendar_color_button;

src/gui/calendar-management/gcal-new-calendar-page.ui

@@ -180,14 +180,16 @@
   </template>
 
   <!-- Credentials popover -->
-  <object class="GtkWindow" id="credentials_dialog">
+  <object class="AdwWindow" id="credentials_dialog">
     <property name="title" translatable="yes">Credentials</property>
     <property name="modal">True</property>
     <property name="hide-on-close">True</property>
     <property name="default-width">350</property>
     <property name="default-height">150</property>
 
-    <child type="titlebar">
+    <property name="content">
+      <object class="AdwToolbarView">
+        <child type="top">
           <object class="GtkHeaderBar">
             <property name="show-title-buttons">False</property>
 
@@ -212,8 +214,7 @@
 
           </object>
         </child>
-
+        <property name="content">
-    <child>
           <object class="GtkBox">
             <property name="orientation">vertical</property>
             <property name="margin-top">12</property>
@@ -280,7 +281,9 @@
             </child>
 
           </object>
-    </child>
+        </property>
+      </object>
+    </property>
   </object>
 
   <!-- Headerbar buttons -->