WL#4299: Stored Routines: use the new metadata cache

Affects: Server-6.1   —   Status: Assigned   —   Priority: Medium

Abandon connection-local caching scheme of stored routines and use the global
cache implemented in WL#3292 instead.
Use metadata locks implemented in WL#3726 to protect the elements of the cache
from concurrent DDL.

This worklog:
Solves BUG#12093