Generate HasPrincipalKey on relationship if necessary

[DavidBoone]

Took a crack at fixing https://github.com/loresoft/EntityFrameworkCore.Generator/issues/574 and came up with this.

It resolved the issue I was having with my SQLite test case, but I'm not super familiar with the code-base so I can't be confident it's the right solution in all cases. Please review carefully!

If nothing else I hope it serves as a handy starting point for a more robust implementation.