rotate
Rotates the binary representation of this UInt128 number right by the specified bitCount number of bits. The least significant bits pushed out from the right side reenter the number as the most significant bits on the left side.
Rotating the number right by a negative bit count is the same as rotating it left by the negated bit count: number.rotateRight(-n) == number.rotateLeft(n)
Rotating by a multiple of UInt128.SIZE_BITS (128) returns the same number, or more generally number.rotateRight(n) == number.rotateRight(n % 128)