AssetManager2: Implement IDMAP support

This enables RRO (runtime resource overlays) with AssetManager2

Test: make libandroidfw_tests
Test: out/host/<platform>/nativetest64/libandroidfw_tests/libandroidfw_tests --testdata=frameworks/base/libs/androidfw/tests/data
Change-Id: Id8079104faefbfaa3f4017d8f7ee1a8968f151a2