Update overscroll and toast UI

Overscroll updates:
Same shape, but smaller radius (doesn't come as far into the view)
and more translucent (max 15% instead of 50%). Overall, more subtle.

Toast updates:
Light background, smaller, dark font, closer to the bottom of the
container.

Test: manual unit tests. Also:
cts test ToastTest for toast changes
cts test EdgeEffectTests for EdgeEffect changes (adding some tests to
known-failures for now, due to brittle golden-image failures - see
CL ag/2596621)
Bug: 30563264  Refresh toast visuals for Android ODR
Bug: 63010438  Tweaks to overscroll animation
Change-Id: I0fac6322b0b81d030c8d174852c134211290bbea