LatinIME: Add a configuration for preview view transient test

Preview Views are only rendered when they not still in a
transient state.

This test is based on properties of the display and some new
large displays may require that this test be tuned.  Expose an
overlay'able tunable to allow this tuning to be applied.

Change-Id: I387a1f5f17b6d0f2085c4831fb2813064331e00c