[Todo] ANF-based pattern matching

Now we only have GNF-based pattern matching. However, in some cases we do need pattern matching with ANF IR.

Specifically, the passes introduced by #23 can be significantly refactored/simplified with ANF pattern matcher.

Start by reading the existing GNF-based pattern-matching implementation and the passes introduced by issue #23; no specific files or entry points are named in this issue. Determine the required ANF IR matching behavior and how those passes should use it. Done means ANF pattern matching is supported and the affected passes are refactored or simplified accordingly.

Written by the indexing model from the issue text.