Extend test/DebugInfo/local-vars.swift.gyb to include more scenarios.

New data types include various forms of enums, tuples, large structs,
generics, and existentials. New contexts include switch statements
closure captures and (also) tuples.

This uncovered at least one bug so some of the CHECKs are commented out.

<rdar://problem/36031959>

Author: adrian-prantl