This PR renames `ForeignKeyReferenceOnDelete` to `ForeignKeyAction`.
The name was too long. Also, `ON DELETE` and `ON UPDATE` referential
actions are the
same. This name makes it clearer that we are reusing this enum for both
options.

Extracted from #628

…`create_table` (#640)

This PR reuses the same object from constraint definition of
`create_table`.
Also, match type gets its dedicated definition, as it can be reused in
multiple
places as well.

Extracted from #628

This PR adds support for creating not validated constraints in `ALTER
TABLE` statements.
I am adding unit tests in a follow-up PR, when `ConstraintSQLWriter` is
moved into a separate file.
Either way, it is not used anywhere yet to avoid conflicts with other FK
related
changes in future PRs.

Extracted from #628

This PR adds the missing `match_type` configuration to
`ConstraintSQLWriter`.
Tests are coming in a follow-up PR when the `ConstraintSQLWriter` gets
its own file.

Extracted from #628

…`create_constraint` (#653)

Now more foreign key options are supported:
* `match_type` in column definitions and in `create_constraint`
* `on_update` in column definitions and in `create_constraint`
* `on_delete_set_columns` in `create_constraint`
* `on_update` in inline FK definitions in a column's `references`
* `match_type` in inline FK definction in a column's `references`

Extracted from #628. The only
remaining part of that PR is adding support in `sql2pgroll`. 🎉