Merges together multiple indexed seqs
Used for inserting items into sorted vectors, using the index provided by NavigableArrayOps.bs
If there is an element at idx (where again it's a NavigableArray.bs style idx) this method will either replace if with replaceFn(xs(idx)) is defined, with that defined value or remove it if replaceFn is not defined there.
CIISeqOps OWNS the array it is wrapped!
CIISeqOps OWNS the array it is wrapped!
DOES NOT COPY THE ARRAY SO BE CAREFUL, CHANGES TO THE UNDERLYING ARRAY WILL DO BAD BAD THINGS.
Used various vector operations