before this change, we rely on the default-generated fmt::formatter
created from operator<<. but this depends on the
`FMT_DEPRECATED_OSTREAM` macro which is not respected in {fmt} v10.
this change addresses the formatting with fmtlib < 10, and without
`FMT_DEPRECATED_OSTREAM` defined. please note, in {fmt} v10 and up,
it defines formatter for classes derived from `std::exception`, so
our formatter is only added when compiled with {fmt} < 10.
in this change, `fmt::formatter<invalid_mutation_fragment_stream>`
is added for backward compatibility with {fmt} < 10.
Refs scylladb#13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18053
6bd0be71ab