Favor xmlunit-assertj3 instead of xmlunit-assertj

[scordio]

As an outcome of xmlunit/xmlunit#203, xmlunit-assertj3 was created to better integrate with the AssertJ 3.x API (Java 8 based), while the existing xmlunit-assertj remains compatible with AssertJ 2.x (Java 7 based and on maintenance mode).

Knowing that Spring Boot 2 was already requiring Java 8 as the minimum requirement, I think it would be a more sensible choice to include xmlunit-assertj3.

[wilkinsona]

Thanks, @scordio. Rather than replacing the dependency management for xmlunit-assertj, which will break people's builds when they upgrade, I think we should add dependency management for xmlunit-assertj3 alongside it. Looking at this also helped me to notice that dependency management for xmlunit-jakarta-jaxb-impl is also missing for Boot 3.0. I've taken care of things in #32998, #32999, and, #33000. Thanks again for bringing this to our attention.

[scordio]

Thanks for the detailed explanation, @wilkinsona. I approached this topic quite quickly and didn't give enough weight to the breaking change, let alone the possible backporting 🙂