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)
TMDM-7768: "xsd:duration type doesn't work"

Maps xsd:duration to java.lang.String (in turn mapped to varchar in database).
Updates unit test accordingly.
(https://jira.talendforge.org/browse/TMDM-7768)
Merge branch 'maintenance/5.6'