apex respects stem of java_library modules

apex now respects stem of java_library modules.

As a follow-up we need to suppor the same for other types of modules.

Exempt-From-Owner-Approval: cherry-pick from AOSP

Bug: 157638999
Test: m
Merged-In: Iaf5023020b5440f1ffd4f5414b5a7864655fc22a
(cherry picked from commit a62aa239)
Change-Id: Iaf5023020b5440f1ffd4f5414b5a7864655fc22a