Automatically export bootclasspath_fragment stubs from sdk

This change makes the tag that is used to add dependencies onto stubs
from the bootclaspath_fragment module cause the dependency to be
automatically exported from the sdk. If the dependency is a
java_sdk_library then it will be as if it was added to the
java_sdk_libs property, otherwise it will be as if it was added to the
java_header_libs property instead.

Bug: 177892522
Test: m nothing
Change-Id: I97010c4342dd39415dba81a4395db7831410436e