am 596451c: AI 147796: Add widget design guidelines to new UI Guidelines

Merge commit '596451ce46f6c7c49e399d3b4025d0f42c5cb979' into donut

* commit '596451ce46f6c7c49e399d3b4025d0f42c5cb979':
  AI 147796: Add widget design guidelines to new UI Guidelines area in dev guide.