Merge changes from topics "expandable-border", "expandable-interactive-size" into tm-qpr-dev

* changes:
  Introduce the FadingBackground modifier
  Make clickable Expandables have a minimum (interactive) size (1/2)
  Add support for borders in Expandable (1/2)
  Reconcile Expandable.kt on master/tm-qpr-dev-plus-aosp and tm-qpr-dev