Add C API bindings for DB::CompactFiles (fixes #11915)

[lihasgupta]

RocksDB's C++ API has DB::CompactFiles(), which compacts a caller-specified set of SST files into a target level. The C API had no equivalent, making this operation inaccessible from C programs.

rocksdb_compaction_options_t
A new opaque struct wrapping CompactionOptions. It is distinct from the existing rocksdb_compactoptions_t, which wraps CompactRangeOptions and is used by rocksdb_compact_range*.

• rocksdb_compaction_options_create()
• rocksdb_compaction_options_destroy()
• rocksdb_compaction_options_set/get_compression()
• rocksdb_compaction_options_set/get_output_file_size_limit()
• rocksdb_compaction_options_set/get_max_subcompactions()
• rocksdb_compaction_options_set/get_allow_trivial_move()
• OMITTED canceled: requires std::atomic*, not C-safe
• OMITTED output_temperature_override: Temperature enum is internal

rocksdb_compact_files()
Compacts the given input files into the target level using the default column family.

rocksdb_compact_files_cf()
Same, but with an explicit column family handle