Swift: Hide LValueType in the main AST

[MathiasVP]

:til: that lvalues are annotated with an LValueType in the AST. I don't think this is a very user-friendly type to have pop up in the "main AST" (it certainly surprised me!).

This PR hide those LValueTypes from the main AST.

[redsun82]

Why is this causing so many changes in the dataflow test?

[MathiasVP]

Why is this causing so many changes in the dataflow test?

This is because we now recognize more PostUpdateNodes. The dataflow library detects which arguments might be an object whose fields could be modified by a function call. This is done by this check here. Previously, those getType calls returned an LValueType which made the check fail.

Now, it can be argued that some of these PostUpdateNodes actually shouldn't be there. But we can fix that in a later PR. That won't have any affects on results.

[redsun82]