Code style cleanup

[ChrisJollyAU]

Bit of a cleanup of the code style

• Added .editorconfig so that any instance in VS uses the same style suggestions
• Updated strings to raw string literals where necessary (mostly the AssertSql in the tests - new tests were already using it but not old tests)
• Use range indexers
• Use collection expressions
• Start implementing implicit usings
• Use primary constructors
• Use pattern matching

EFCore.Jet.Data

• Further work on nullable reference types (it's the only project not with it enabled)
• Throw a better error if it can't find any compatible drivers installed
  • Occurs when provided with a connection string that doesn't specify any driver/provider, and we search for what is installed to find something. See #239