Improve EZP-23333: Content object build speed using SPI Cache

Use ContentType from SPI (straight from cache) instead of using API for
internal use as API version needs lots of build and load logic.

Do this for Content and Relation object build (DomainMapping).
Merge pull request #982 from ezsystems/faster_object_build

Improve EZP-23333: Content object build speed using SPI Cache