We want to avoid adding regular `id`s to Annotation-elements, since that means that they become "linkable" through the URL hash in a way that's not supported/intended. This could end up clashing with "named destinations", and that could easily lead to bugs; see issue 11499 and PR 11503 for some context.
Rather than using `id`s, we'll instead use a *custom* `data-element-id` attribute such that it's still possible to access the Annotation-elements directly.
Unfortunately these changes required updating most of the integration-tests, and to reduce the amount of repeated code a couple of helper functions were added.
