Fix EZP-21909: ObjectStates are not set for copied Content

This PR resolves issue https://jira.ez.no/browse/EZP-21909

Sub-task of https://jira.ez.no/browse/EZP-21897

This fixes a bug where default Content states were not set for copied Content and enables indexing of Content states in Solr Storage.
SetContentState slot in Solr Storage is also implemented to enable reindexing of Content when Content state is changed.

Tests:
* implemented unit tests for `ContentService::copyContent()`
* integration regression tests (not enabled here as they still contain failures on other issues, see sub-tasks)

Additional:
* fixed test dependencies in unit tests for ContentService
* some code reusage in unit tests for ContentService after implementing tests for `ContentService::copyContent()`