Extend C API to expose base db of transaction db

[remicalixte]

Add rocksdb_transactiondb_get_base_db and rocksdb_transactiondb_close_base_db functions to the C API modeled after rocksdb_optimistictransactiondb_get_base_db and rocksdb_optimistictransactiondb_close_base_db:

rocksdb/include/rocksdb/c.h

Lines 2711 to 2716 in ca50ccc

	extern ROCKSDB_LIBRARY_API rocksdb_t*
	rocksdb_optimistictransactiondb_get_base_db(
	rocksdb_optimistictransactiondb_t* otxn_db);
	extern ROCKSDB_LIBRARY_API void rocksdb_optimistictransactiondb_close_base_db(
	rocksdb_t* base_db);

With this pair of functions, it is possible to get a rocksdb_t * from a rocksdb_transactiondb_t *. The main goal is to be able to use the approximate memory usage API, only accessible to the rocksdb_t * type:

rocksdb/include/rocksdb/c.h

Lines 2821 to 2833 in ca50ccc

	extern ROCKSDB_LIBRARY_API rocksdb_memory_consumers_t*
	rocksdb_memory_consumers_create(void);
	extern ROCKSDB_LIBRARY_API void rocksdb_memory_consumers_add_db(
	rocksdb_memory_consumers_t* consumers, rocksdb_t* db);
	extern ROCKSDB_LIBRARY_API void rocksdb_memory_consumers_add_cache(
	rocksdb_memory_consumers_t* consumers, rocksdb_cache_t* cache);
	extern ROCKSDB_LIBRARY_API void rocksdb_memory_consumers_destroy(
	rocksdb_memory_consumers_t* consumers);
	extern ROCKSDB_LIBRARY_API rocksdb_memory_usage_t*
	rocksdb_approximate_memory_usage_create(rocksdb_memory_consumers_t* consumers,
	char** errptr);
	extern ROCKSDB_LIBRARY_API void rocksdb_approximate_memory_usage_destroy(
	rocksdb_memory_usage_t* usage);

[jowlyzhang]

LGTM, thanks for the PR!

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@jowlyzhang merged this pull request in 6628ff1.