Extract shared utils so they can be used without depending on core Shell.

This is in preparation of making the Animation library a dependency of
Shell. The Animation lib itself needs to depend on these utilities to
handle transitions, so pulling it out into its own target solves
dependency cycles.

Fix: 321724947
Flag: NA
Test: both soong and gradle builds work
Change-Id: I1c461d976a5d3a72e3cd86fc8b904224c403382f