The PR introduces shard_repair_task_impl which represents a repair task
that spans over a single shard repair.
repair_info is replaced with shard_repair_task_impl, since both serve
similar purpose.
Closes#12066
* github.com:scylladb/scylladb:
repair: reindent
repair: replace repair_info with shard_repair_task_impl
repair: move repair_info methods to shard_repair_task_impl
repair: rename methods of repair_module
repair: change type of repair_module::_repairs
repair: keep a reference to shard_repair_task_impl in row_level_repair
repair: move repair_range method to shard_repair_task_impl
repair: make do_repair_ranges a method of shard_repair_task_impl
repair: copy repair_info methods to shard_repair_task_impl
repair: corutinize shard task creation
repair: define run for shard_repair_task_impl
repair: add shard_repair_task_impl
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