Port OpenJDK8 unsigned methods

Adds following methods with tests:

java.lang.Byte#toUnsignedInt
java.lang.Byte#toUnsignedLong
java.lang.Integer#compareUnsigned
java.lang.Integer#divideUnsigned
java.lang.Integer#parseUnsignedInt
java.lang.Integer#remainderUnsigned
java.lang.Integer#toUnsignedLong
java.lang.Integer#toUnsignedString
java.lang.Long#compareUnsigned
java.lang.Long#divideUnsigned
java.lang.Long#parseUnsignedLong
java.lang.Long#remainderUnsigned
java.lang.Long#toUnsignedString
java.lang.Short#toUnsignedInt
java.lang.Short#toUnsignedLong

Bug: 28582540
Change-Id: I715f146ba45f15f588a2aed38e2b85cebe98f747