Query: Skip constants in GROUP BY

[kosinsky]

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If Linq expression uses constants in GroupBy skip these constants in SQL GROUP BY to avoid "Each GROUP BY expression must contain at least one column that is not an outer reference" SQL exception.

Fixes #14152

• Tests for the changes have been added (for bug fixes / features)
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[smitpatel]

This is not the correct way to solve this.

[kosinsky]

OK, I did more diggin and found that I could achieve the same goal by not adding constant in SelectExpression.GroupBy collection in first place. Am I on right track or I should go even higher upstream?

I've updated PR to show that approach.

[smitpatel]

@kosinsky - Thank you for contribution. The 2nd approach seemed more appropriate.