[ASTERIXDB-1949][FUN][ING] Function usage check refactoring in feed - user model changes: no - storage format changes: no - interface changes: yes Removed several interefaces for maintaining reference count. Added getFunctions and getFeeds method for MetadataNode.
1. Change the usage check from reference count to scan feed connections in all dataverses. 2. Add test case for drop dataverse which has function that is being used in other dataverse. This operation should be blocked. 3. Fix small bug in apply function metadata which the function dataverse was not recorded properly.
Fix function usage check in feed 1. Add reference count field to Function entity. 2. Add reference count check when drop function. 3. Increate reference count when apply function to feed. Decrease the reference count when disconnect feed. 4. Add test cases for drop function that is being used and drop function that is no longer in use.