Make bootanim multi-display aware

Also, some refactoring of existing code.

Flag: com.android.graphics.bootanimation.flags.multidisplay
Bug: 269510347
Test: Manual (build, flash, reboot in folded and unfolded states)
Change-Id: Ieb360f47cc38cab90b1eca471b0e773e303f88e2
4 files changed