Gets the non-conversion expression corresponding to this node, if any.
This predicate only has a result on nodes that represent the value of
evaluating the expression. For data flowing out of an expression, like
when an argument is passed by reference, use asDefiningArgument instead
of asExpr.
If this node strictly (in the sense of asConvertedExpr) corresponds to
a Conversion, then the result is the underlying non-Conversion base
expression.