Add new user setup command banchan for module building.

It currently uses TARGET_BUILD_APPS just like tapas, but the use case is
different and it may diverge more in the future.

Test: banchan com.android.art
Test: banchan help
Test: banchan
Test: hmm
Bug: 179779520
Change-Id: Iae718e65a2a7212c741c397e03c6f9a6d5ee8951