Add public API TextView.isHorizontallyScrolling

The original purpose is to remove @hide annotation on
TextView.getHorizontallyScrolling, but the function name conflicts
with our API naming convention. So, I created public API
isHorizontallyScrolling instead.

Bug: 117520716
Test: atest TextViewTest
Test: make offline-sdk-docs
Change-Id: I79666c8920cdfcb9dc68ae3701c6599f063df5fd