Make MAPPINGS_CACHE_SIZE configurable

[hehechen]

The MAPPINGS_CACHE_SIZE is 4 by hard coding. Can we make it configurable? In some scenarios, the lib mappings cache miss will cause performance degrade, especially in the scenario that the debug sections are compressed. For example: https://github.com/pingcap/tiflash/issues/6347#issuecomment-1333038382 Some users may want to increase MAPPINGS_CACHE_SIZE to trade memory for performance improvement.