On the previous interface between Group Replication plugin and
Performance Tables there was memory allocation which was being
passed to server side. This memory allocation should be avoided,
also it can cause problems when it is released from a different
entity that allocated it.

To avoid that issues, now the interface uses callbacks that are
invoked by plugin to send information to Performance Schema tables,
or other callers. The callback implementations are the ones that
are responsible to allocate new memory, if needed.

We also changed the definition of
performance_schema.replication_group_members table member_state
column to be a arbitrary string, being now the plugin the full
responsible of its values. The values continue to be: ONLINE,
OFFLINE and RECOVERING.