tools/scylla-sstable.cc has 3.5k SLOC, out of which this class alone is 1K. Extract into own hh and cc. Since this class was already using pimpl, the header remains nice and small.
Code cleanup, no backport needed.
Closesscylladb/scylladb#26064
* github.com:scylladb/scylladb:
tools: extract json_mtuation_stream_parser to its own hh,cc files
tools/scylla-sstable: fix indentation
tools/scylla-sstable: prepare for extracting json_mutation_stream_parser