[ci skip] Fix inaccurate callback documentation

[Wittiest]

Summary

Fixes #42457

Other Information

The callback de-deduplication logic currently happens at the time callbacks are set on a model. A fix that would implicitly solve a few issues around de-duping would be to apply the following for all callbacks accepting symbolized method names:

• Rather than front-load de-duplication, have a Set created during the application of each callback (ex: on_update) and dynamically de-duplicate invocations of a specific method here. This would implicitly stop duplicate predicate methods from running in the cases of overlapping if and unless conditions while also allowing for distinct if and unless conditions to pass in the same symbolized method name for the same callback method.

[ghiculescu]

I would drop “symbolized” - “method name” should be fine. Do you think it’s worth mentioning that if you use the block form it’s fine to use both?

[Wittiest]

@ghiculescu I think it's fine to avoid that detail because people can immediately see that if they want to call the same method, they can just use after_save_commit in the documentation below.

This is more about correcting the documentation which incorrectly makes developers think they cannot use both of these callbacks. The case where devs want to use both of these callbacks instead of after_save_commit would be when they are calling different methods.

[zzak]

@Wittiest Could you squash your commits please? 🙏

[Wittiest]

@zzak Done :)