Improve ScrollFeedbackProvider API Javadoc

Reworded the summary statement to clarify that the feedback is feedback
given to the user, and that it may depend on the configuration of the
InputDevice that generated the scroll event. Also added a small
paragraph to give an example of feedback that may be provided by this
interface.

Bug: 260290361
Test: n/a
Change-Id: I8e21fbff8f87384581df1722ba4ba919b5395486