Add bootclasspath_fragment.

Note that the contents of the bootclasspath_fragment are added as
dependencies to an apex, so there is no need to duplicate them in
java_libs.

Bug: 180105615
Test: atest CtsClasspathsTestCases
Change-Id: Ibbedc8e4b15801f4a11e3155c453db0e51944995
1 file changed