Expressions need type annotations in the parse trees

[MDoerner]

We should annotate the expression nodes and all their sumnodes with types. This could either be a type interface or simply a string. (The latter would allow the annotation even before resolving references.)

This would be a first step towards code-path analysis. Moreover, this would allow for new inspections and to hugely simplify existing ones like the ObjectNotSetInspection.

[retailcoder]

The Rubberduck.Parsing.Preprocessing namespace quite possibly includes a lot of reusable stuff, especially for evaluating If conditions.