The code in `multishard_mutation_query.cc` implements the replica-side of range scans and as such it belongs in the replica module. Take the opportunity to also rename it to `multishard_query`, the code implements both data and mutation queries for a long time now.
Code cleanup, no backport required.
Closesscylladb/scylladb#26279
* github.com:scylladb/scylladb:
test/boost: rename multishard_mutation_query_test to multishard_query_test
replica/multishard_query: move code into namespace replica
replica/multishard_query.cc: update logger name
docs/paged-queries.md: update references to readers
root,replica: move multishard_mutation_query to replica/
5b40d4d52b