Generate guid's for primary key client side

[ChrisJollyAU]

For primary key's that are a Guid, always generate the Guid client side in EFCore.Jet rather than by the external engine.

Reason for this is that we can't get the generated Guid back after insert.
With a normal numeric identity counter, Jet allows you to do SELECT @@identity and it will return the last value inserted to the identity. Unfortunately, there is nothing like that for a Guid - the above statement just returns the integer 0

Hence, we can solve this by the client-side Guid generation