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
Merged-In: Ib69eea9d79cc83b8e3fc29919a29f071e1ec17b5
Change-Id: Ib69eea9d79cc83b8e3fc29919a29f071e1ec17b5
(cherry picked from commit 524c82c0)