Add a test API PackageManager#MODULE_APEX_NAME (2/n)

This API is used by the GTS to check mainline modules distributed as
apk-in-apex are included in the whitelist.

Bug: 148386485
Test: N/A (included in another CL)
Change-Id: I25b1c0703e3f345756a5ba91de070025042714f4
2 files changed