Lookup right hand side processing was compiling query compilers which happened
to work by chance as SQLCompiler defines a as_sql() method with two optional
parameters albeit it doesn't expect the same type of arguments.

Thanks Preston Timmons for review.

Thanks Tim Graham for the review.

Regression in f5c62957.

This reverts commit e62ea0bb since it
broke multi-column __in lookups and _meta.order_wrt on Oracle.

Django's test runners no longer discover doctests.

Queries could potentially be resolved in cases where ordering matter.

Thanks Tim Graham for the review.

The is_iterator() function was removed in 2456ffa4.

read() and write() were removed in 68a890e7.

Refs #23919 -- Used "raise from" instead of __cause__ in reraising backend-specific database exceptions.

Thanks Tim Graham for the review.

Thanks Claude Paroz and Tim Graham for reviews.