Let numeric buttons rely more on touch-down on dialpad

This change lets the dialpad shows tentative digit during touch-down.
Because of some other problems we're still using touch-up for
emitting DTMF sound.

TESTED:
- Call usual phone numbers
- Try basic swipe and see a tentative number is erased
-- (e.g. Press '5' and start swiping, seeing '5' being erased during
    the horizontal swipe). User should not hear DTMF sound.
- Try Voicemail by long-pressing '1'.
- Try entering '+' by long-pressing '0'. It should remove tentative
  '0'.

Bug: 5749440
Change-Id: Id5332e643a6476efceb044f7d372118ffdc77377