apex: checks min_sdk_version for preview/current

If we don't check "current", it won't be checked even in the finalized
branch.

If we don't check "preview", it should be done during the SDK
finalization. It'd be better done before the SDK finalization regarding
that setting min_sdk_version is to get approval from deps library owners.

Bug: 177833148
Test: m (soong tests)
Change-Id: I712b61cfe5a134fbb69c73956d26fb3a1e5c011e