XWIKI-9508: SOLR does not allow to match documents matching specific values in multiple xwiki properties
* Use 'class' instead of 'object' to index the type of objects a document has, because 'class' is already used when indexing objects and object properties, and also because we wan't to avoid having two facets when the user searches for all results/entity types. We can still use 'object:Space.SomeClass' in a Solr query because I added an alias so it will be automatically rewritten to 'class:Space.SomeClass'.