Match on enum arm collection using tree structure

This is a preparation step to supporting enum matching on inner enum variants.
To support multi level matching we need to address different enum variants will have different parameters, therefor a tree structure, VariantMatchTrees, is introduced.

Coverage of all variants is done by checking if all tree leaves are full and not empty, where empty cases are missing subvariants.

commit-id:978a80be

Author: eytan-starkware