The function splits the source mutation into multiple
mutations so that their size does not exceed the
max_size limit. The size of a mutation is calculated
as the sum of the memory_usage() of its constituent
mutation_fragments.
The implementation is taken from view_updating_consumer.
We use mutation_rebuilder_v2 to reconstruct mutations from
a stream of mutation fragments and recreate the output
mutation whenever we reach the limit.
We'll need this function in the next commit.
db1afa0aba