ViewRootImpl: Correct opaque flag usage

In performTraversals, "params" may be null. In this case we were
not passing params to the WM indicating no changes (an obscure
artifact of the protocol).  In R the WM would simply ignore this
however our updateOpacity logic in S is treating null as "translucent"
it seems easiest to just pass mWindowAttributes directly avoiding
the null case. While the opacity was broken, it seems an animation
was added to StartingSurfaceDrawer which depends on having a translucent
window. We also update this code to request a transparent pixel format
as would have been required in the R API.

Bug: 186555833
Test: Existing tests pass
Change-Id: I180bf1796bbb4b7049ae9811f674f31014c2a400