Rearchitect navigation expansion to happen in translation, not preprocessing

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See #32957 for some context (these two issues can probably be considered duplicates).

See partial work in https://github.com/dotnet/efcore/tree/RemoveNavExpansion. This does a lot of the basic work of handling navigations in the translation phase, commenting out the preprocessor; but quite a bit of work still remains.

Note that in this branch, non-JSON owned navigations and regular navigations are now handled in the same code path, which is a considerable simplification compared to EF's current state (where regular navigations are expanded in preprocessing, and owned navigations in a separate code path in relational translation, where we can distinguish between JSON and non-JSON owned navigations).