Add version to vendor variants

Vendor variant is now divided into several vendor.{version} variants,
depending on their intended usages:

vendor.{BOARD_VNDK_VERSION}: vendor and vendor_available modules
vendor.{PLATFORM_VNDK_VERSION}: VNDK modules in the source tree
vendor.{snapshot_ver}: VNDK snapshot modules

This also affects exported module names from Soong to Make. But to
maintain backward compatibility, ".{BOARD_VNDK_VERSION}" suffix will not
be emitted for modules having version BOARD_VNDK_VERSION, so that vendor
modules still can be referred as-is.

Bug: 65377115
Bug: 68123344
Test: clean build and boot blueline
Change-Id: Ib9016a0f1fe06b97e9423fd95142653a89a343fa