Fix tab carousel flicker issues

Cases fixed:
- Animation of the tab carousel causes a brief jump
at the end of the animation because the vertical scroll
listener is trying to move the tab carousel to a different
Y coordinate at the same time

- Horizontally scrolling the tab carousel causes it to
get into an "in-between" state where it is out of sync
with the ViewPager (there is also flicker on each tab
because the alpha values are wrong)

- Rotating from phone landscape updates page to phone portrait
was never implemented (didn't scroll the tab carousel to the
right tab)

- Rotating from phone portrait updates page to phone landscape
would cause a noticeable flicker where the page would slide to
the left so the correct page was selected because it was scrolled
when executing a Runnable

Fix issues by scrolling the HorizontalScrollView if necessary
in onLayout(). Consume touch down/up events on the tab carousel.
Add flag to know when the tab carousel is already animating.

Bug: 5220668
Change-Id: Icecaa99b43682111fb7c7d201a059b3962b00cd6