Add support for GNOME 40

Extension Information

• Shell Version: GNOME 40.alpha
• Extension Version: 105
• Install method: extension.gnome.org
• OS: Fedora 33 with GNOME 40 alfa installed via

sudo dnf copr enable haeckerfelix/gnome-shell-40 && sudo dnf update

Describe the bug

GNOME 40 is already in alpha and it forces the usage of GTK4 for extensions dialogs, please consider adding support for it.

The extensions seems to work so far but when you try to open the preferences dialog of your awesome extension it crashes with the message below 👇

Gtk.BuilderError: /home/fran/.local/share/gnome-shell/extensions/openweather-extension@jenslody.de/weather-settings.ui:15:39 Invalid property: GtkWindow.window_position

Stack trace:
  initWindow@/home/fran/.local/share/gnome-shell/extensions/openweather-extension@jenslody.de/prefs.js:131:21
  wrapper@resource:///org/gnome/gjs/modules/script/_legacy.js:82:27
  _init@/home/fran/.local/share/gnome-shell/extensions/openweather-extension@jenslody.de/prefs.js:121:14
  wrapper@resource:///org/gnome/gjs/modules/script/_legacy.js:82:27
  buildPrefsWidget@/home/fran/.local/share/gnome-shell/extensions/openweather-extension@jenslody.de/prefs.js:1116:17
  _init@resource:///org/gnome/Shell/Extensions/js/extensionsService.js:209:40
  OpenExtensionPrefsAsync/<@resource:///org/gnome/Shell/Extensions/js/extensionsService.js:122:28
  asyncCallback@resource:///org/gnome/gjs/modules/core/overrides/Gio.js:132:22
  run@resource:///org/gnome/Shell/Extensions/js/dbusService.js:177:20
  main@resource:///org/gnome/Shell/Extensions/js/main.js:19:13
  run@resource:///org/gnome/gjs/modules/script/package.js:222:19
  start@resource:///org/gnome/gjs/modules/script/package.js:206:8
  @/usr/share/gnome-shell/org.gnome.Shell.Extensions:1:17
  

Please update you extension to keep enjoying using it. Thanks for your incredible work!