Make possible to respond to image derivative creation

The Needs Review Queue Bot → tested this issue. It either no longer applies to Drupal core, or fails the Drupal core commit checks. Therefore, this issue status is now "Needs work".

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The patch does apply on 10.1.x. Setting to Needs review and retesting.

I'm proposing another patch, which has (almost) the same code as yours, but on a different class: Instead of invoking the hook on ImageStyleDownloadController::deliver(), I invoke it on ImageStyle::createDerivative() to make sure that the hook is invoked also when the derivative is created by other methods (for example through the image_style_warmer module).

Fixed PHPCS problems.

This issue is being reviewed by the kind folks in Slack, #needs-review-queue-initiative. We are working to keep the size of Needs Review queue [2700+ issues] to around 400 (1 month or less), following Review a patch or merge request → as a guide.

Adding a new api will require a change record. An example is usually very helpful.

Issue summary should be updated to more clearly define the proposed solution and api change.

Will also need test coverage of the api working

Updated the patch for the 11.x branch, and created a draft change record.

After some thought, I added another argument in the hook, which is the id of the image style. Although by default it can be derived from the derivative image uri, there can be cases where this is not possible (for example a custom implementation of an external file system like s3fs.)

Updated also the change record.

Sending to NW for the open tags

Issue summary update and test coverage

Looking at the MR new api should be typehinted also.

Added type hints to api, added a test. Not sure about the issue summary update, isn't the change record enough?

No issue summary is separate from a CR. Recommend using default issue template

Is it ok now?

Summary yes

But tests are failing too btw.

Removed a useless assertion that was breaking the tests.

Setting it back to needs work, the tests are failing, although they succeed locally. I will investigate further...