Add support for merged / moved tags

[dennisfisch]

TagManager automatically resolves the cq:movedTo property when fetching cq:tags of a resource. This resolution also happens when calling adapTo(Tag.class) on any resource that has such a property, returning the successor tag.

I originally wanted to implement mergeTag() and moveTag() as well, but basically hit a wall when considering this operations does not only shuffle individual tags around, but also handles whole subtrees of tags and creates copies and movedTo / backlinks relationships between them.

[stefanseifert]

can you create a PR from the work you did at https://github.com/dennisfisch/io.wcm.testing.aem-mock/tree/feature/resolve-cq-movedto-tags? then i can have a closer look at it.