Several issues when creating new mobile project

Creating a new Mobile project with Stack-based navigation and Material Dark

results in several issues. See this screenshot:

1. The UI is not using Dark theme. It works if I change the top-level item in `App.qml` to be `ApplicationWindow` instead of `Window`. But then, QtDS complains that `ApplicationWindow` is not supported as top-level.
2. The font used by Qt for Android does not support Unicode entry `\u2630` (i.e. ☰) from the `ToolButton`. That character is displayed properly in Qt for macOS.
3. `Text` item content is rendered at the right scale but the `Label` item from the `ToolBar` has the font way too small
4. Same scale issues are visible in the `ItemDelegate` from the `Drawer`:
   
5. The character is rendered as an orange box with a white arrow (in desktop it is shown as a white arrow):