Make sure that classpath fragment contents appear in make vars.

The source of truth for what jars are in BOOTCLASSPATH and
SYSTEMSERVERCLASSPATH is make; adding a classpath fragment in soong
with a new jar in the contents without having it declared in make
is wrong (excluding test apexes).

Bug: 191369843
Test: m nothing
Change-Id: Ifd313776ee7ad206031244534ed3870126e4f835