Add UNSAFE_DISABLE_HIDDENAPI_FLAGS to skip hiddenapi processing

Setting environment variable UNSAFE_DISABLE_HIDDENAPI_FLAGS=true
will skip the build step which annotates dex files with information
about public and non-public API membership. This is meant to speed
up incremental local builds.

USE AT OWN RISK: Dex files built with this flag will execute with
hidden API access checks disabled and therefore may exhibit different
behaviour compared to production code.

WARNING: Some JARs cannot be compiled with this flag as ART hardcodes
hidden API access flags of intrinsified methods. Attempting to compile
dex files containing such methods will trigger an assertion.

Test: UNSAFE_DISABLE_HIDDENAPI_FLAGS=true mmm frameworks/base
Bug: 113278235
Bug: 112388925
Change-Id: I51fe99ab53e1bb2aa0db64b22a321dd1e1ed47e1