sql: improve type determination for column meta

In most cases we don't assign and store type of node of expression AST
(except for constant literals).  To determine type of node  we use
sql_expr_type() function, which implements logic of quite simple
recursive tree traversal. Before this patch we set type of node after
code generation in sqlExprCodeTarget() without any traversal. This
approach is way worse even then sql_expr_type(). So, to improve accuracy
of type determination, let's always call that method and remove type
assignment in sqlExprCodeTarget().

Closes #4126