RFR 8138632: Sparse array does not handle growth of underlying dense array

[Hannes Wallnoefer]

Please review JDK-8138632: Sparse array does not handle growth of 
underlying dense array

http://cr.openjdk.java.net/~hannesw/8138632/
This includes some cleanup (static methods marked final, removal of 
toIndex parameter in ArrayData.canDelete that was never used).

Thanks,
Hannes