Fix issue with the unhandled drag flag not being respected

- We should always only call the unhandled drag callback if the drag
  flag is set (even if there is a launchable intent in the clip data)
- Also renaming some tests now that the unhandled drag listener is
  a more generic global drag listener

Bug: 320797628
Test: atest DragDropControllerTests
Change-Id: I6e50745ec64373926c99b2c4f562bd23f434708c