Adding operations to reflected Renderscript class

Renderscript expose its native types back to the Android
system through a set of classes defined within the renderscript
package. These classes provides no easy mean to manipulate
data they represent. It would be convinient to be able to manipulate
the data stored within an allocation via these classes directly
instead of having to marshall them into native Java objects.

This commit adds such operations to the existing exposed vector types.

Change-Id: I1845df1368a82f0d39b36416c83938c7160f6a3f