Query: improve null conditional simplification

[maumar]

In NullCheckRemovingExpressionVisitor we have logic to simplify expressions like:

a == null ? null : a.Foo

into simple property access when on relational (null propagation is automatic)
However for some complex cases we miss the optimization and produce overly complicated.

e.g.:

ctx.Points.Select(
                    e => new
                    {
                        e.Id,
                        Distance = e.Point == null ? (double?)null : new Point(0, 1).Distance(e.Point)
                    })

produces:

SELECT ""p"".""Id"", CASE
    WHEN ""p"".""Point"" IS NULL THEN NULL
    ELSE Distance(GeomFromText('POINT (0 1)'), ""p"".""Point"")
END AS ""Distance""
FROM ""PointEntity"" AS ""p""

rather than expected:

SELECT ""e"".""Id"", Distance(GeomFromText('POINT (0 1)'), ""e"".""Point"") AS ""Distance""
FROM ""PointEntity"" AS ""e""

[maumar]

related to #18555

[maumar]

note that some Sqlite functions don't propagate nullability (e.g. all spatial functions returning bool)

[smitpatel]

@maumar - This is actually not possible to do easily.

• It is not valid for all providers
• It depends if the function is actually getting translated to server for given provider
• If the server side translation actually propagates nulls.

May be best place to do so would be post translation in SQL where we can may be remove Case test if it is null check if the result is somehow null propagating.

The cost may not worth the value it would provide. (User can always write without null check and cast result to nullable type)