Fix and test vendor public libraries for product modules

Vendor public libraries are checked for product modules, but never
reached because the VNDK check occurs first, and wouldn't work anyways
because vendor_public_library did not have the product_available
property.  Reorder the rewrite checks and add VendorProperties, and
add a test.

Bug: 178231622
Test: vendor_public_library_test.go
Change-Id: Idbd2802fbd134d22c30600762cb0465633703506

cc/vendor_public_library.go

@@ -155,6 +155,7 @@ func vendorPublicLibraryFactory() android.Module {
 
 	module.AddProperties(
 		&stub.Properties,
+		&module.VendorProperties,
 		&library.MutatedProperties,
 		&library.flagExporter.Properties)