add directional scroll for accessibility action in NumberPicker

Test: Twisted talkback code to perform scroll down when scroll forward
is called. Verfied that scroll down is successfully performed in the
framework code and the number picker behaves correctly. Also verifed the
scroll up/down actions are correctly added to AccessibilityNodeInfo.
Bug: 136277517
Change-Id: I540d2ed3bf4e6b733668853182bd38faa8545997