Vectorized over str and with respect to each code point
in pattern and replacement.
If pattern and replacement consist of a different number
of code points, then the extra code points in the longer of the two
are ignored, with a warning.
If code points in a given pattern are not unique, the
last corresponding replacement code point is used.
Time complexity for each string in str is
O(stri_length(str)*stri_length(pattern)).