[bs_lib] Improved anchor link scrolling

This feature is coming from bs_lib dependency module but is documented here for now.

This is doing a couple of things:

• Enabling smooth anchor scrolling,
• Works for both anchors click on the current page and anchor links loading directly from URL,
• Can handle top sticky elements by calculating their height and then taking that into calculations.

To activate improved anchor link scrolling go to Administration > Configuration > System > BS Lib and there you will see the next setting options:

Enable anchor scrolling and set other options per your use case.