check_target_files_vintf: Support flattened apexes

Flattened apexes are extracted and copytree()'d to /apex directory to
simulate "activation" on device.

Bug: 242314000
Bug: 239055765
Test: m otapackage # target with "flattened" apexe
Change-Id: I90cc37b5f64ebad1e15f6fc5fa245d0f5955095d

Change-Id: I7e8c3fdf8e4620344d23cee0de509e574206ad9b