Replace with_labels() and apply_labels() in ORM/Core

Replace with_labels() and apply_labels() in ORM/Core

Replace :meth:`_orm.Query.with_labels` and
:meth:`_sql.GenerativeSelect.apply_labels` with explicit getters and
setters ``get_label_style`` and ``set_label_style`` to accommodate the
three supported label styles: ``LABEL_STYLE_DISAMBIGUATE_ONLY`` (default),
``LABEL_STYLE_TABLENAME_PLUS_COL``, and ``LABEL_STYLE_NONE``.

In addition, for Core and "future style" ORM queries,
``LABEL_STYLE_DISAMBIGUATE_ONLY`` is now the default label style. This
style differs from the existing "no labels" style in that labeling is
applied in the case of column name conflicts; with ``LABEL_STYLE_NONE``, a
duplicate column name is not accessible via name in any case.

For legacy ORM queries using :class:`_query.Query`, the table-plus-column
names labeling style applied by ``LABEL_STYLE_TABLENAME_PLUS_COL``
continues to be used so that existing test suites and logging facilities
see no change in behavior by default, however this style of labeling is no
longer required for SQLAlchemy queries to function, as result sets are
commonly matched to columns using a positional approach since SQLAlchemy
1.0.

Within test suites, all use of apply_labels()  / use_labels
now uses the new methods.    New tests added to
test/sql/test_deprecations.py nad test/orm/test_deprecations.py
to cover just the old apply_labels() method call.  Tests
in ORM that made explicit use apply_labels()/ etc. where it isn't needed
for the ORM to work correctly use default label style now.

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Fixes: #4757
Change-Id: I5fdcd2ed4ae8c7fe62f8be2b6d0e8f66409b6a54