Added java_system_modules_import

A prebuilt version of java_system_modules. It does not import the
generated system module, it generates the system module from imported
java libraries in the same way that java_system_modules does. It just
acts as a prebuilt, i.e. can have the same base name as another module
type and the one to use is selected at runtime.

Bug: 142940300
Test: m nothing
Change-Id: I126db49d18294fcd6e2b7ad0237f83e9c2fdef7a