Treat src=name filegroups as handcrafted targets

This is groundwork for allowlist v2, as such targets are still
effectively referencable via their file syntax; thus, rdep targets of
these filegroups should still be treated as convertible.

Fixes: 302025822
Test: Unit test update
Change-Id: I93445ff75e7c0570530725d086e47c1532833c06