Perform hidden API encoding in bootclasspath_fragment

Previously, the apex content info was populated with hidden API encoded
dex jars retrieved directly from the java module. This change retrieves
the unencoded dex jars from the java module, encodes them and then
stores the result in the apex content info.

Bug: 179354495
Test: m com.android.art com.android.ipsec com.android.os.statsd com.android.conscrypt
      - verify that this does not change the contents of the apex files
Change-Id: Ib1b6eb8b62ac50e03b9e0d07c877ca70bb6f6d25