Spring 7 - XML configuration no longer supported

### Issue description

Spring has stated that xml driven configuration (at least for MVC) is not going to be supported in Spring Framework 7 (it will be there, but Spring won't support it). However, they're separately adding a programmatic way to add beans. We'll likely need to rework the bean builder as a result since it's ultimately backed by xml.

https://github.com/spring-projects/spring-framework/wiki/Spring-Framework-7.0-Release-Notes#deprecations

Read the Spring Framework 7 release notes linked in the issue, then trace Grails' bean builder and its XML-backed configuration. Determine the scope of replacing or adapting that builder for Spring 7's programmatic bean-registration approach; done means the builder works without relying on unsupported XML configuration.

Written by the indexing model from the issue text.