[notification] allow themes to indicate how long a notification is open #9856
Description
Describe your motivation
It would be nice to be able to do some custom animation that indicates how long the notification stays open, like a progress bar.
Describe the solution you'd like
Add a CSS custom property to the component host which indicates the duration, e.g. <vaadin-notification style="--duration: 6;">.
A raw number gives more flexibility than an actual duration like 6s, so that the number can be used to define other properties as well (like size for example).
Describe alternatives you've considered
No response
Additional context
No response