event-widget: Sizing overhaul

This reworks how GcalEventWidget handles its sizing by:

• using an AdwSqueezer to automatically fall back from the vertical to the horizontal mode (simplifying the code)
• allow narrow labels to wrap on chars in vertical mode (helping the widget to be narrow)
• explicitely allow the labels to overflow the widget and hidding the overflow (helping the widget to be narrow)
• ensuring we allocate the widgets at least what they request (fixing errors)

Before

Tons of errors like this:

(gnome-calendar:2): Gtk-CRITICAL **: 12:53:13.508: Allocation width too small. Tried to allocate 32x107, but GcalEventWidget 0x56540498bcf0 needs at least 51x107.

After

No error message.