multishard_mutation_query: generalize query code w.r.t. the result builder used
multishard_mutation_query: generalize query code w.r.t. the result builder used

We want to add support to building `query::result` directly and reuse
the code path we use to build reconcilable result currently for it.
So templatize said code path on the result builder used. Since the
different result builders don't have a source level compatible interface
an adaptor class is used.

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla