Have property_service create a serialized property_contexts file

Instead of requiring each process to parse the property contexts files
in libc initialization, this change has property_service parse these
files one into a serialized trie, which the property code in libc can
then directly interpret for mapping property names to their associated
SELinux context.

Bug: 36001741
Test: boot bullhead, walleye, run unit tests

Change-Id: If67073d56e800b3ca667fb5322e6b993e7d810f6