Fix Value::evaluate_cmp_with_literal between Decimal and Literal::Num…

[panarch]

…ber,

Handle Value::Decimal & Literal::Number branch - convert value to bigdecimal and run cmp.
Rewrite test-suite/ data-type/decimal tests, add a comparison test case.

e.g.

CREATE TABLE Foo (v DECIMAL);
INSERT INTO Foo VALUES (1), (2);

SELECT v FROM Foo WHERE v > 0;

WHERE v > 0 was not working.

[coveralls]

Pull Request Test Coverage Report for Build 5704628120

• 44 of 44 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 98.56%

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Totals
Change from base Build 5704033435:	0.007%
Covered Lines:	46206
Relevant Lines:	46881

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💛 - Coveralls