Add SelectBase.exists() method as it seems strange this is
not available already.  The Exists construct itself does
not provide full SELECT-building capabilities so it makes
sense this should be used more like a scalar_subquery.

Make sure stream_results is getting set up when yield_per
is used, for 2.0 style statements as well.  this was
hardcoded inside of Query.yield_per() and is now moved
to take place within QueryContext.

Change-Id: Icafcd4fd9b708772343d56edf40995c9e8f835d6

The operator changes are:

* `isfalse` is now `is_false`
* `isnot_distinct_from` is now `is_not_distinct_from`
* `istrue` is now `is_true`
* `notbetween` is now `not_between`
* `notcontains` is now `not_contains`
* `notendswith` is now `not_endswith`
* `notilike` is now `not_ilike`
* `notlike` is now `not_like`
* `notmatch` is now `not_match`
* `notstartswith` is now `not_startswith`
* `nullsfirst` is now `nulls_first`
* `nullslast` is now `nulls_last`

Because these are core operators, the internal migration strategy for this
change is to support legacy terms for an extended period of time -- if not
indefinitely -- but update all documentation, tutorials, and internal usage
to the new terms.  The new terms are used to define the functions, and
the legacy terms have been deprecated into aliases of the new terms.

Fixes: #5435
Change-Id: Ifbd7cb1cdda5981990243c4fc4b4ff467dc132ac

Fixed structural compiler issue where some constructs such as MySQL /
PostgreSQL "on conflict / on duplicate key" would rely upon the state of
the :class:`_sql.Compiler` object being fixed against their statement as
the top level statement, which would fail in cases where those statements
are branched from a different context, such as a DDL construct linked to a
SQL statement.

Fixes: #5656
Change-Id: I568bf40adc7edcf72ea6c7fd6eb9d07790de189e

Improved support for column names that contain percent signs in the string,
including repaired issues involving anoymous labels that also embedded a
column name with a percent sign in it, as well as re-established support
for bound parameter names with percent signs embedded on the psycopg2
dialect, using a late-escaping process similar to that used by the
cx_Oracle dialect.

* Added new constructor for _anonymous_label() that ensures incoming
  string tokens based on column or table names will have percent
  signs escaped; abstracts away the format of the label.

* generalized cx_Oracle's quoted_bind_names facility into the compiler
  itself, and leveraged this for the psycopg2 dialect's issue with
  percent signs in names as well.  the parameter substitution is now
  integrated with compiler.construct_parameters() as well as the
  recently reworked set_input_sizes(), reducing verbosity in the
  cx_Oracle dialect.

Fixes: #5653

Change-Id: Ia2ad13ea68b4b0558d410026e5a33f5cb3fbab2c

These attributes will be removed in SQLAlchemy 2.0.

Also alters the deprecation message to qualify the
type of object correctly.  this in turn requires changes
in the warnings filter and deprecation tests.

Change-Id: I5779d9813e88f42e5db0c7b5e3ffff1d1535c203

The :paramref:`_schema.MetaData.bind` argument as well as the overall
concept of "bound metadata" is deprecated in SQLAlchemy 1.4 and will be
removed in SQLAlchemy 2.0.  The parameter as well as related functions now
emit a :class:`_exc.RemovedIn20Warning` when :ref:`deprecation_20_mode` is
in use.

Added new parameter :paramref:`_automap.AutomapBase.prepare.autoload_with`
which supersedes :paramref:`_automap.AutomapBase.prepare.reflect`
and :paramref:`_automap.AutomapBase.prepare.engine`.

Fixes: #4634
Fixes: #5142

Change-Id: Iaabf9b481931e2fb68b97b5954c32e65772a298e

The :class:`_schema.Table` class now raises a deprecation warning
when columns with the same name are defined. To replace a column a new
parameter :paramref:`_schema.Table.append_column.replace_existing` was
added to the :meth:`_schema.Table.append_column` method.

The :meth:`_expression.ColumnCollection.contains_column` will now
raises an error when called with a string, suggesting the caller
to use ``in`` instead.

Co-authored-by: Federico Caselli <cfederico87@gmail.com>
Change-Id: I1d58c8ebe081079cb669e7ead60886ffc1b1a7f5

Fixed issue where a plain pickle dumps call of the :class:`_sql.Over`
construct didn't work.

Fixes: #5644
Change-Id: I4b07f74ecd5d52f0794128585367012200a38a36