Move accessibilityHeader from TextView to View

I put it on TextView to try to scope it as narrowly
as possible, but an ImageView could be a heading, as
could a LinearLayout that holds a TextView (like a
preference).

Bug: 77726494
Test: atest CtsAccessibilityServiceTestCases
Change-Id: I9313ce6de25b5893db450f23499b151a4f08afda