refactor: add revision context to AutogenerateDiffsDetected so that wrappers may...

refactor: add revision context to AutogenerateDiffsDetected so that wrappers may make other formatting of the diff

### Description
As discussed in #1597, AutogenerateDiffsDetected should hold contextual information so that command can be wrapped for another format (CI, pre-commit hook...)

### 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)

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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #1598
Pull-request: https://github.com/sqlalchemy/alembic/pull/1598
Pull-request-sha: 7799320ad3c1a1bd769254d610288c97f85cb345

Change-Id: Id08bc52a0586063f177736a36a61f96232459f1c