[merp] Add API method that whitelists all native libraries

[merp] Add API method that whitelists all native libraries

This is so that complex consumers such as Visual Studio for Mac can forego attempting to enumerate all loaded libraries, register them one at a time and potentially keep the list updated

Commit migrated from https://github.com/mono/mono/commit/40a8d88d8e0178d333c53ea3cb0e53363c2304ba