Set a better default size (height and width) for the event editor dialog

These are still hardcoded instead of measuring the available space,
but it's better than nothing in the meantime.

Decent WMs size the window correctly if width/height exceed the screen.

Also, allow the Notes field to expand vertically, to fill the space.

Fixes https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/602

src/gui/event-editor/gcal-event-editor-dialog.ui

@@ -2,8 +2,8 @@
 <interface>
   <template class="GcalEventEditorDialog" parent="GtkDialog">
     <property name="modal">True</property>
-    <property name="default-width">450</property>
-    <property name="default-height">500</property>
+    <property name="default-width">700</property>
+    <property name="default-height">1000</property>
     <property name="use_header_bar">1</property>
     <property name="destroy_with_parent">True</property>
     <property name="hide-on-close">True</property>
@@ -140,6 +140,7 @@
                 <child>
                   <object class="GcalNotesSection" id="notes_section">
                     <property name="sensitive" bind-source="GcalEventEditorDialog" bind-property="writable" bind-flags="default" />
+                    <property name="vexpand">True</property>
                   </object>
                 </child>
               </object>