Add sample layouts for toolbar style widgets

[shamalip]

Contains two flavors of responsive toolbar layouts:

1. Search toolbar: Focuses on presenting a prominent search entry point along with 4 additional buttons for other frequently used actions. Drops as a 2x2 where search bar is on the top and buttons below it.
2. Toolbar with app header: Presents an app brand logo, a header icon for most frequently used action, and 4 other frequently used actions. Drops as 4x1 toolbar showing all items in a row.

These layouts use Glance's scaffold component that allows us to

1. Fill bounds
2. Use system defined widget corner radius
3. mark our background with id/background to help with animations

The buttons fill the available space as well - which along with breakpoints enable us to use the widget space efficiently.

CL also includes glance android studio previews at the defined breakpoints.

[shamalip]

+@ashnohe for repo approval

[yrezgui]

Great work @shamalip! The screenshots are nice and the codebase well explained.