EF Core: Add value generation support (auto-increment, sequences, GUIDs)

[DaveRMaltby]

Summary

The EF Core providers lack proper value generation infrastructure. While the ADO.NET layer supports identity columns via LAST_INSERT_ID(), the EF Core layer doesn't register custom IValueGeneratorSelector or IValueGeneratorCache services.

What's Needed

IValueGeneratorSelector

Select appropriate value generators based on property configuration:

• Auto-increment integers (already partially supported via LAST_INSERT_ID)
• GUID generation for Guid primary keys
• Temporary value generation for tracking entities before save

Value Generation Strategies

• ValueGeneratedOnAdd — generate value on insert (identity columns, GUIDs)
• ValueGeneratedOnAddOrUpdate — generate on insert or update (computed columns, timestamps)
• Proper HiLo or Sequence patterns (may not apply to file-based, but should be explicitly unsupported)

Impact

Without proper value generation, context.SaveChanges() may fail to correctly handle auto-generated primary keys, or may not set them back on the entity after insert.

Standard Reference

• Value Generation
• IValueGeneratorSelector