Java/C++/C#: Add DataFlowErasedType class

[hvitved]

This PR adds a new parameter, DataFlowErasedType, to the implicit signature of the shared data flow implementation. The motivation is to be able to distinguish erased types from normal types: currently this is not done anywhere, but it will be in the C# implementation of type pruning.

[aschackmull]

AFAICS DataFlowType is then no longer used? Then I think it'll be cleaner to just reuse DataFlowType to mean what DataFlowErasedType currently means. If you then want to use distinct names in the C# implementation you should have both DataFlowType and DotNet::Type available to you.

[aschackmull]

Perhaps we could even get rid of getErasedRepr in the implicit signature and replace it with DataFlowType getDataFlowType(Node n) { getErasedRepr(n.getType()) }

[hvitved]

AFAICS DataFlowType is then no longer used? Then I think it'll be cleaner to just reuse DataFlowType to mean what DataFlowErasedType currently means. If you then want to use distinct names in the C# implementation you should have both DataFlowType and DotNet::Type available to you.

You are right; I have changed DataFlowErasedType back to DataFlowType.