Rather than force all dispatchers to be templated on a device adapter,
instead use a TryExecute internally within the invoke to select a device
adapter.
Because this removes the need to declare a device when invoking a
worklet, this commit also removes the need to declare a device in
several other areas of the code.
-Changing the existing CellLocator.h to CellLocatorHelper.h,
it's used by CellLocatorTwoLevelUniformGrid.h
-Changing unit tests and worklets that use CellLocator.h to use CellLocatorHelper.h
