Summary:
* Add metadata related structs and functions in C API, including
  - `rocksdb_get_column_family_metadata()` and `rocksdb_get_column_family_metadata_cf()`
     that returns `rocksdb_column_family_metadata_t`.
  - `rocksdb_column_family_metadata_t` and its get functions & destroy function.
  - `rocksdb_level_metadata_t` and its and its get functions & destroy function.
  - `rocksdb_file_metadata_t` and its and get functions & destroy functions.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10207

Test Plan:
Extend the existing c_test.c to include additional checks for column_family_metadata
inside CheckCompaction.

Reviewed By: riversand963

Differential Revision: D37305209

Pulled By: ajkr

fbshipit-source-id: 0a5183206353acde145f5f9b632c3bace670aa6e