deapexer: add support for extracting content of APEX image

This can be used by signer in order to re-sign APKs inside APEX.

Test: deapexer extract system/apex/shim/com.android.apex.cts.shim.v2.apex /tmp/bar
Bug: 138429615
Change-Id: I733bfb57b028979b4a6c0d6245f4d495ed3a9671
2 files changed