Created by: davidxiasc
Addresses https://github.com/facebook/buck/issues/2400
Currently, building Messages extensions with buck will not generate the Messages app icon correctly. This is because in order to do so, actool needs to know what product type it is creating an asset catalog + app icon for.
This change funnels the product type from apple_bundle into AppleAssetCatalog and AcToolStep so that actool is called with --product-type <product type> (needs to be com.apple.product-type.app-extension.messages for Messages extensions).