HPCC-9746 Don't match expressions to constant transform values.

If the tranform for a PROJECT contains self.x := 10, and the expression
it is moved over also refers to 10, it should not be substitued with
projected.x.

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4736 from ghalliday/issue9746

HPCC-9746 Don't match expressions to constant transform values.

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>