Add support for Projections in logic tests

[thorfour]

We recently discovered that the logic tests don't support projections when I implemented projections during aggregations here: #252

[asubiotto]

To implement this, we probably need to add another switch case in the following function:

frostdb/sqlparse/visitor.go

Line 48 in e628ed5

func (v *astVisitor) leaveImpl(n ast.Node) error {

To figure out what the ast node is, the best way is to step through using a debugger while running a logictest sub test with a projection.

[palash25]

could this be solved by iterating over SelectFields and applying a projection for each? something like this?

case *ast.FieldList:
		for _, f := range expr.Fields {
			v.builder.Project(f.Expr)
		}

[asubiotto]

I haven't looked at this closely enough to know, but this would make sense, although Project takes multiple expressions so we'd probably want to push them on the expression stack and then pop them all off when encountering a FieldList if that makes sense. I'm also wondering about the case when we don't want to call builder.Project (i.e. as we currently do).

[thorfour]

This was added by #258