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

Fixes: #5661

### Description
Fixes reflection of composite primary keys to maintain the correct column order in the MSSQL
and SQLite dialects.

Closes: #5662
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5662
Pull-request-sha: b568dec7070b4f3ee46a528bdf16fb237baade2a

Change-Id: I452b23cbf7f389c4a0a34cffce5c32498efe37d2

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

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

Using strings to represent relationship names in ORM operations such as
:meth:`_orm.Query.join`, as well as strings for all ORM attribute names
in loader options like :func:`_orm.selectinload`
is deprecated and will be removed in SQLAlchemy 2.0.  The class-bound
attribute should be passed instead.  This provides much better specificity
to the given method, allows for modifiers such as ``of_type()``, and
reduces internal complexity.

Additionally, the ``aliased`` and ``from_joinpoint`` parameters to
:meth:`_orm.Query.join` are also deprecated.   The :func:`_orm.aliased`
construct now provides for a great deal of flexibility and capability
and should be used directly.

Fixes: #4705
Fixes: #5202
Change-Id: I32f61663d68026154906932913c288f269991adc

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