TMDM-7777: "Metadata:timestamp  in the view search  return null label"

Fixes issue in projections when a metadata field is not aliased and query handler uses full text optimizations.
Amend existing test for timestamp projection with a query to trigger FT optimization.
Clean up in ViewSearchResultsWriter (reuses type name constants).
(https://jira.talendforge.org/browse/TMDM-7777)