Handle DVs that mismatch a prop's expected type

If a Snak contains a DataValue of a type different from
the value type expected by the property's data type,
don't fail, but handle gracefully.

Bug: 63299
Change-Id: I41b489ff5b5ea474861922a8c50b214e67851319
Merge "Handle DVs that mismatch a prop's expected type"