Make basic EF scenarios work under aggressive trimming

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.NET 7.0 is enabling aggressive trimming mode for console applications (but not for other workloads, e.g. ASP.NET). This makes all EF console applications break immediately when published as trimmed.

This issue is about ensuring minimal functionality of EF console apps with aggressive trimming. Some caveats:

• Some specific patterns may be necessary in user code in order to ensure that certain user types/members in the model aren't trimmed away. We will document these caveats.
• EF will by no means be fully trimming-compatible, and no guarantees are given to the correct working of user applications. This is a best-effort work item; full compatibility with trimming will be explored in future versions of EF.

/cc @DamianEdwards @davidfowl @vitek-karas