ART: Add support for special handlers in sigchainlib

Add support for a special managed handler in sigchainlib that
will be called as the first user handler.

Use this support for native bridge v2. Extend test 115-native-bridge
to test the functionality.

Bug: 20217701

(cherry picked from commit 03c2cc89)

Change-Id: I78cc01fbdabe169154ff6b94c9f3ddb95b5c7448