Get prop aliases through their type, not raw value

If an alias was set for a prop and a value was passed through __set__
for that alias, the __get__ for that alias would return the raw value
instead of putting it through type conversion (if one was set).

Closes-Bug: 1392580
Change-Id: Id6c2cfccd2fba182f75e6b7dbd3bcd0c5aacafa7