Configurable hidden API exemptions.

Extend the existing hidden_api_blacklist_exemptions config to support a
list of API signature prefixes to exclude from hidden API enforcement.

Push this list down to the zygote process when that process is created,
and when the list changes. This minimizes overhead, but should also ensure
that all new processes get the latest whitelist.

Test: $ adb shell settings put global hidden_api_blacklist_exemptions \
Test:    Landroid/view/RemoteAnimationDefinition\\\;:Landroid/app/ActivityManager\\\$TaskDescription\\\;
Test: Manually verify logcat output from app which uses named APIs
Bug: 73337509

(cherry picked from commit 2c6f97d4)

Merged-In: Ib1245b69da4dac50c6968f1be62f1a74591dc433
Change-Id: I7b590f272fdcfcda5f18e216788ac34bc58beaed