Add utility function to find shard replacements

Streaming RPC coordinators can use this function to generate a list of
shard replacements that is suitable to be passed to
fabric_util:stream_start/4.

BugzId: 20423
Provide replacement shards in map views

BugzId: 20423
Provide replacement shards in reduce views

BugzId: 20423
Provide replacement shards in changes feeds

BugzId: 20423