Allow aliased() to be passed to Query.select_entity_from().

Allow aliased() to be passed to Query.select_entity_from().

An :func:`.aliased()` construct can now be passed to the
:meth:`.Query.select_entity_from` method.   Entities will be pulled
from the selectable represented by the :func:`.aliased` construct.
This allows special options for :func:`.aliased` such as
:paramref:`.aliased.adapt_on_names` to be used in conjunction with
:meth:`.Query.select_entity_from`.

Additionally rewrote the docstring for :meth:`.Query.select_entity_from`,
including starting with explicit use of :func:`.aliased` as the
usual idiomatic pattern.  An example using text().columns() is added
as well as the use case from :ticket:`3933` using name matching.

Change-Id: If7e182965236993064a2a086e3b6d55a4f097ca8
Fixes: #3933