Query: TypeCompatibility chart for inference

[smitpatel]

When we generate SQL like [c].[DoubleColumn] * 5 = 88 the inferred TypeMapping for constants become DoubleTypeMapping. In order to print out constant we cast value to double which throws following exception.
Message: System.InvalidCastException : Unable to cast object of type 'System.Int32' to type 'System.Double'.

Given operator upcasting, we don't need to use DoubleTypeMapping to print 5/88, we can just use int (or whatever type it is). But in order for us to do that, we need the logic in inference.

[roji]

Note impact on set operations, where we have different store types coming out of the two sides but it's OK since they're implicitly convertible (see #16813 (comment)).

We may even consider a chart detailing explicit convertibility, to know which store types can be cast to which other types. This would allow us to add SQL casts if necessary.

[smitpatel]

Explicit would be bad idea from provider side because if unknown types encountered you wouldn't know. Implicit side much better that you can be certain you don't need cast. In the absence of which it would be always casted.

[roji]

Note additional interesting case: Npgsql translates NewArrayExpression, and infers type mappings across all the provided elements. Heterogeneous/incompatible elements cause an exception (the array must be of a single PG type), but we do support heterogeneous elements when they're implicitly convertible to one another (e.g. same base type with different facet, or even varchar(15) and text). This is currently "hacked" here, but a type compatibility chart would make this better.