New component: time span picker

[Cosmatevs]

This pull request contains:

• a new component, similar to the date picker in appearance, behavior, and configuration,
• tests for the new component,
• component style tweaks for free themes,
• demos for the new component, covering most configuration properties,
• an update of the form field component demo to include the new component,
• a new helper component: PopupOrInline, which makes it much easier to handle displaying a part of the component as a popup or just inline,
• a new enum: TimeSpanUnit used to indicate time unit fields that should be shown in the picker
• a fix for the clear button position in the date picker inside a form field – because the implementation of that clear button is the same as in the new component
• additional 'time' tag for the date picker in the demo list – to make it easier to find it if you want just a time picker.

Things I couldn't do:

• component style tweaks for premium themes,
• documentation.

To take into consideration:

• implementing a time span filter for the data grid component.
• implementing some solutions from my closed pull request Form field: styling fixes and tweaks #1958, especially my comment from 2025-02-28,
• reimplementing popup/inline handling in the date picker using the PopupOrInline component in a similar way. The current solution requires a lot of micromanaging (mostly js calls) to make it work and seems prone to breaking.