[cdac] Fix building of method signature names for class type variables

[elinor-fung]

• Use type instantiation (instead of method) for formatting signature with class type variables
• Handle creating instantiation for arrays to pass to signature formatting helper

Examples:

-System.Collections.Generic.Dictionary`2[[System.Int32, System.Private.CoreLib],[System.UInt64, System.Private.CoreLib]].Add(!!0, !!1)
+System.Collections.Generic.Dictionary`2[[System.Int32, System.Private.CoreLib],[System.UInt64, System.Private.CoreLib]].Add(Int32, UInt64)

-System.Object[].Set(Int32, !!0)
+System.Object[].Set(Int32, System.Object)

[dotnet-policy-service]

Tagging subscribers to this area: @tommcdon
See info in area-owners.md if you want to be subscribed.