EZP-23116: Change SPI Content Search Handler to return ContentInfo

https://jira.ez.no/browse/EZP-23116

Does not affect API, idea is to avoid having to return the full objects for:
- faster internal use
- avoid performance degradation with many languages

It should also improve performance generally as it performs less sql calls.
( further reductions can be archived by making sure it can use cached instance of languageHandler )
Should be updated in the second argument in the `getMock` call above.
Also callback needs to be updated to return `ContentInfo`.