Add TARGET_PLATFORM_VERSION to lunch

lunch can now take combos in the form:
$TARGET_PRODUCT
$TARGET_PRODUCT-$TARGET_BUILD_VARIANT
$TARGET_PRODUCT-$TARGET_BUILD_VARIANT-$TARGET_PLATFORM_VERSION

If all 3 are not specified the unspecified ones will take the
default values provided by the build system (eng, and currently
OPR1).

In addition, error handling for invalid products, variants and
versions is moved to the build system.

Bug: 34972208
Test: build/make/tests/envsetup_tests.sh
Change-Id: Ib0aaa98633448ba9bd8df911704c9cb3a8ebbe85