Make getStateDescription() in View none final

Do not make getStateDescription final, since it can cause
compatibility issues with existing derived classes that define
a getStateDescription. Also replaced call to
getContentDescription() to mContentDescription. This is because
if a subclass overrides it, we don't want it to affect the value
used in accessibility service (cause divergence in accessibility
event and accessibilityNodeInfo).

Bug: 143652980
Test: no needed
Change-Id: I36c94c85eb258b3c9474090d841c925331d22d73