Export hidden api related types and fields

This will export some hidden api related types and fields so they can
be used from outside the java package. This is needed to allow a follow
up change to move the TestPlatformBootclasspath_Fragments from the java
to the apex package.

Bug: 179354495
Test: m nothing
Change-Id: Ib69eea9d79cc83b8e3fc29919a29f071e1ec17b5