Make IQueryOptimizer/QueryOptimizer non-internal

[austindrenski]

In the provider for PostgreSQL, we are exploring some complex translations via IQueryOptimizer/QueryOptimizer which provide an extensibility point for injecting expression visitors.

However, we are wary of replacing services from the EF Core Internal namespaces.

Would it be possible to move IQueryOptimizer and QueryOptimizer out of the internal namespace?

current:  Microsoft.EntityFrameworkCore.Query.Internal
proposed: Microsoft.EntityFrameworkCore.Query

Related:

• Map List<T> operations to PostgreSQL arrays (old) npgsql/efcore.pg#431
• Add extensibility point for IQueryOptimizer npgsql/efcore.pg#444

/cc @roji

[ajcvickers]

We are going to consider this as part of the general 3.0 query work, so adding a link to #12795.

[austindrenski]

@ajcvickers Thanks for the update—much appreciated!

[smitpatel]

The optimizations from IQueryOptimizer has been moved to QueryOptimizer which is public.