Introduce new constant for double tap gesture rotation hint.

As discussed in ag/1192965/ we have a special case for rotation
animation selection in launch from double tap. This was set to
ROTATION_ANIMATION_CROSSFADE as the goal was just to avoid
ROTATION_ANIMATION_ROTATE on the viewfinder surface and
seamless rotation in launch scenarios was initially descoped. Now we
are aiming at fixing this though, and ROTATION_ANIMATION_CROSSFADE
does not quality for seamless rotation. ROTATION_ANIMATION_JUMPCUT
also would not be a good choice because in the situation that the
rotation occurs before the app starting window appears, then we would
jump cut from unrotated wallpaper to rotated app, I think we want
a crossfade in this scenario. To this end introduce and use a new @hide constant
ROTATION_ANIMATION_SEAMLESS which qualifies for seamless but falls back
to CROSSFADE if seamless can't occur.

Bug: 30171992
Change-Id: If1945b17b5159be4cd5ba0b139d6bea9f7fcca33