Remove ``typing.Self`` workaround, now using :pep:`673` for most methods
that return ``Self``. Pull request courtesy Yurii Karabas.

Fixes: #9254
Closes: #9255
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/9255
Pull-request-sha: 2947df8ada79f5c3afe9c838e65993302199c2f7

Change-Id: Ic32015ad52e95a61f3913d43ea436aa9402804df

Corrected the fix for :ticket:`7664`, released in version 2.0.0, to also
include :class:`.DropSchema` which was inadvertently missed in this fix,
allowing stringification without a dialect. The fixes for both constructs
is backported to the 1.4 series as of 1.4.47.

Fixes: #7664
Change-Id: I509b7500ee496ac1e444ea2096c2a02520167e6d

Fixed stringify for a the :class:`.CreateSchema` DDL construct, which would
fail with an ``AttributeError`` when stringified without a dialect.

Fixes: #7664
Change-Id: Ifc1769604bc5219c060f5112f7bdea0f780f1a1c

type annotation somehow decided that TableClause doesn't have
primary key fields which is not the case at all.   In particular
the "views" recipe relies on TableClause so adding a restriction
like this does not make any sense.

It seems the issue was to open this up for typing, by allowing
TableClause out as far as ddl.sort_tables() typing is passing
for now.   Support it out in get_bind() etc.

Fixes: #9071
Change-Id: If0e22e0e7df7bee0ff4b295b0ffacfbc6b7a0142

Change-Id: I625af65b3fb1815b1af17dc2ef47dd697fdc3fb1

command run is "pyupgrade --py37-plus --keep-runtime-typing --keep-percent-format <files...>"
pyupgrade will change assert_ to assertTrue. That was reverted since assertTrue does not
exists in sqlalchemy fixtures

Change-Id: Ie1ed2675c7b11d893d78e028aad0d1576baebb55

Fixes: #8605
Change-Id: I4aec83b9f321462427c3f4ac941c3b272255c088

Added ``if_exists`` and ``if_not_exists`` parameters for all "Create" /
"Drop" constructs including :class:`.CreateSequence`,
:class:`.DropSequence`, :class:`.CreateIndex`, :class:`.DropIndex`, etc.
allowing generic "IF EXISTS" / "IF NOT EXISTS" phrases to be rendered
within DDL. Pull request courtesy Jesse Bakker.

Fixes: #7354
Closes: #8492
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/8492
Pull-request-sha: d107c6ce553bd430111607815f5b3938ffc4770c

Change-Id: I367e57b2d9216f5180bcc44e86ca6f3dc794e5ca

Implemented the DDL event hooks :meth:`.DDLEvents.before_create`,
:meth:`.DDLEvents.after_create`, :meth:`.DDLEvents.before_drop`,
:meth:`.DDLEvents.after_drop` for all :class:`.SchemaItem` objects that
include a distinct CREATE or DROP step, when that step is invoked as a
distinct SQL statement, including for :class:`.ForeignKeyConstraint`,
:class:`.Sequence`, :class:`.Index`, and PostgreSQL's
:class:`_postgresql.ENUM`.

Fixes: #8394
Change-Id: Iee6274984e794f50103451a04d089641d6ac443a

Adds support for comments on named constraints, including `ForeignKeyConstraint`, `PrimaryKeyConstraint`, `CheckConstraint`, `UniqueConstraint`, solving the [Issue 5667](https://github.com/sqlalchemy/sqlalchemy/issues/5667).

Supports only PostgreSQL backend.

### Description

Following the example of [Issue 1546](https://github.com/sqlalchemy/sqlalchemy/issues/1546), supports comments on constraints. Specifically, enables comments on _named_ ones — as I get it, PostgreSQL prohibits comments on unnamed constraints.

Enables setting the comments for named constraints like this:
```
Table(
   'example', metadata,
   Column('id', Integer),
   Column('data', sa.String(30)),
   PrimaryKeyConstraint(
       "id", name="id_pk", comment="id_pk comment"
    ),
   CheckConstraint('id < 100', name="cc1", comment="Id value can't exceed 100"),
   UniqueConstraint(['data'], name="uc1", comment="Must have unique data field"),
)
```

Provides the DDL representation for constraint comments and routines to create and drop them. Class `.Inspector` reflects constraint comments via methods like `get_check_constraints` .
### Checklist
<!-- go over following points. check them with an `x` if they do apply, (they turn into clickable checkboxes once the PR is submitted, so no need to do everything at once)

-->

This pull request is:

- [ ] A documentation / typographical error fix
- [ ] A short code fix
- [x] A new feature implementation
	- Solves the issue 5667.
	- The commit message includes `Fixes: 5667`.
	- Includes tests based on comment reflection.

**Have a nice day!**

Fixes: #5667
Closes: #7742
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7742
Pull-request-sha: 42a5d3c3e9ccf9a9d5397fd007aeab0854f66130

Change-Id: Ia60f578595afdbd6089541c9a00e37997ef78ad3