Solved inline comments get imported and displayed into XWiki

the behavior you describe is exactly what happen for an XWiki annotation which used to match a content that was modified (i.e. a resolved annotation)

Not really. For annotations of XWiki, the altered state is a state set automatically when an annotation is automatically repositioned when the content is modified. A user "resolving" that annotation confirms that the annotation is still valid in the new content, as it was modified, to show it again as a "regular" annotation.
The resolving of inline comments in Confluence has the opposite purpose: to mark that they're not relevant anymore and should not be displayed: this is done for various reasons, but mostly bearing the meaning that the suggestion from that inline comment / annotation was handled. It would be indeed equivalent to deleting the annotation in XWiki, but I don't think we should just skip the import of all resolved inline comments. We could add an option in the importer to skip resolved comments or not.