UInt128 shift implementation doesn't match Kotlin implementation

[mattmook]

Documentation for ULong's shl and shr says:

Note that only the six lowest-order bits of the bitCount are used as the shift distance. The shift distance actually used is therefore always in the range 0..63.

Currently the UInt128 implementation will shift with n >= 128 which will always result in a return value of zero. The ULong implementation looks as though it only shifts by n mod ULong.SIZE_BITS