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 )
Since in handler we do nat pass translations to the gateway, this can result in NotFoundException.
So maybe we solve that problem here or skip the filter here and solve it later.