Merge changes from topics "bundle-expand", "bundle-icon-border", "bundle-summary" into main

* changes:
  Increase gaps of bundle children to 2dp
  Make the border of PreviewIcons transparent
  Allow two lines for the BundleHeaderGuts summary text
  Introduce new gap height between buckets and fix bundle gaps
  Fix bundle guts after dismissal
  Sync BundleHeader STL state with external expand/collapse