Always check VNDK variant identicalness

Previously, we only check VNDK core and vendor variants are identical
when a VNDK library is not declared to have different variants AND the
target has TARGET_VNDK_USE_CORE_VARIANT set.  Therefore, it is fairly
easily to break a TARGET_VNDK_USE_CORE_VARIANT target as it needs to be
tested explicitly.

This change uses the new LOCAL_CHECK_SAME_VNDK_VARIANTS and expands the
check to run regardless of TARGET_VNDK_USE_CORE_VARIANT.  Also adds
support for VNDK-in-product.

Bug: 145157349
Test: Build success for targets with and without
      TARGET_VNDK_USE_CORE_VARIANT.
Test: With the corresponding change in build/make, remove libbinder
      from build/soong/cc/config/vndk.go and check build fails even
      when TARGET_VNDK_USE_CORE_VARIANT is not set.

Change-Id: Iec708b971072e6580f77a03e243b30b89b3b054d