Feature: Support order by SimpleFunction and SimpleExpression

[koenpunt]

To allow ordering results on more than just plain column names I implemented support for SimpleFunctions and SimpleExpressions (created using Expressions.just(..)).

Before if you would try to use a SimpleFunction expression in orderBy it did result in invalid SQL, because it completely omitted the function; ORDER BY ASC.

With these changes you can now use SimpleFunctions and SimpleExpressions as order by expression.

E.g.

orderBy(OrderByField.from(Expressions.just("1"))).asc() => 

   ORDER BY 1 ASC

orderBy(SimpleFunction.create("GREATEST", table1.column("updated_at"), table2.column("updated_at"))).asc() => 

   ORDER BY GREATEST(table1.updated_at, table2.updated_at) ASC

Related: #1113

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[schauder]

Thanks, this merged.

[koenpunt]

Is there a change this is going to be backported to 2.4.x? And then in turn to the spring-data-r2dbc package? Or do we have to wait for spring-boot 3 to be able to use this functionality?