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: Ic80a004135d2747472f98d6c7e666c4acb14badf
Merged-In: Ic80a004135d2747472f98d6c7e666c4acb14badf
1 file changed