Add a Make variable to disable all dexpreopt and dexopt activities.

This change adds a Make variable "OVERRIDE_DISABLE_DEXOPT_ALL", which
disables all dexpreopt and dexopt activities.

This is for faster iteration during development and should never be
enabled for production.

Bug: 309011617
Test: See no dex2oat invocation during build.
Test: Boot and see no dex2oat invocation during boot, except for the
  in-memory boot image for JIT Zygote.
Change-Id: I0193b57fdb18e1fb717f44af81d1cf525f1609ee