Generalize the constant propagation optimization so that it applies on every

Generalize the constant propagation optimization so that it applies on every
WHERE close, not just those that contain a subquery.  This then demonstrates
that the current implementation is inadequate since it does not take into
account collating sequences.

FossilOrigin-Name: 57eb2abd5b270d65be5e0f138f0d46899fa6091df3ba20b0ea7ef04244a15d48