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
Change-Id: Ib1245b69da4dac50c6968f1be62f1a74591dc433