DbFunction tests are missing from the Relational specification tests

[tuespetre]

Self-explanatory -- the SQL Server and Oracle test suites have some pretty thorough UDF test classes but these are not available from the Microsoft.EntityFrameworkCore.Relational.Specification.Tests package. It would be nice if these were available for other providers or libraries to implement.

[pmiddleton]

I can do this if @divega signs off that it is something we want to do.

[ajcvickers]

@pmiddleton Yes, a PR for this would be good.

[pmiddleton]

@ajcvickers Do the Oracle tests run as part of the automated build? If not is there somewhere there who can verify everything passes. I don't have an Oracle setup to test on.

[smitpatel]

@pmiddleton - They are not run as part of automated build. They are also broken at present. @ralmsdeveloper is looking into it currently. We can fix the oracle related issues while merging.