Update target and focus behavior

[mzlock]

• updates the targeting and focus utils to include some changes made to another copy
  • use promises and await when getting new prev/next drop targets
  • FocusManager can take a getActiveElement option
• removes this.actions.publishDragSource() in handleDragStart -- this seemed to be publishing an old copy of the drag source, which caused some positioning issues when an item was dragged more than once

[mzlock]

Will come back to this work soon. I still need to:

• remove yarn stuff, since this uses pnpm now
• double-check that removing this.actions.publishDragSource(); won't break things for other apps using the library