Avoid a potentially expensive reflection-based loop in assertArrayEquals...

..., in the usual case where the arrays are in fact exactly equal.

This is purely a performance optimization so there are no new tests. For primitive arrays, the Arrays.deepEquals method quickly dispatches to the appropriate overload of Arrays.equals, which simply loops over the elements in the expected way. Additionally, Arrays.equals(char[], char[]) is intrinsified by the HotSpot VM so the boost there should be even more substantial.