Shrink mutable byte array to new specified size (in bytes), in the
specified state thread. The new size argument must be less than or
equal to the current size as reported by
getSizeofMutableByteArray#.
Assuming the non-profiling RTS, this primitive compiles to an O(1)
operation in C--, modifying the array in-place. Backends bypassing C--
representation (such as JavaScript) might behave differently.
Warning: this can fail with an unchecked exception.