Popover: add logic to position it completely automatically

[FrancescoCioria]

requirements

anchor="auto" is a good start, but we need the Dropdown to position itself completely automatically which means:

• choose position
• choose anchor

use position and anchor props as defaults in case there enough space for the Popover

specs

for now don't move the arrow dynamically as it complicates the logic a lot. instead search for a combination of postion+anchor that works:

• start with default position and anchor
• if they're not ok
  • position ok; anchor not ok
  • search for anchor that works. if none -> change position and repeat
  • position not ok -> change position and repeat
• if no combination of position and anchor works -> log warning and use defaults

misc

{optional: other useful info}