Empty collection config CRUD operations are inconsistent across the backend.

Problem/Motivation

Doing ::delete, ::deleteAll(), ::rename() on an empty configuration collection results in the different output depending on the backend used.

The consistent methods:

• StorageInterface::exists() - works the same way across storages and collections - if the collection does not exist it will return FALSE.
• StorageInterface::read() - works the same way across storages and collections - if the collection does not exist it will return FALSE.
• StorageInterface::readMultiple() - works the same way across storages and collections - if the collection does not exist it will return an empty array.
• StorageInterface::listAll() - works the same way across storages and collections - if the collection does not exist it will return an empty array.
• StorageInterface::write() - works the same way across storages and collections - if the collection does not exist it will create it.

The inconsistent methods:

• StorageInterface::delete() - FileStorage will throw an exception if the collection does not exist where DatabaseStorage will return FALSE.
• StorageInterface::deleteAll() - FileStorage will return TRUE if the collection does not exist or is empty where DatabaseStorage will return FALSE.
• StorageInterface::rename() - FileStorage will throw an exception if the collection does not exist where DatabaseStorage will return FALSE.

Proposed resolution

Make it consistent...

Remaining tasks

• StorageInterface::delete() - Should return FALSE if collection does not exist.
• StorageInterface::deleteAll() - Should return FALSE if the collection does not exist or is empty
• StorageInterface::rename() - Should return FALSE if the collection does not exist or $name does not exist.

Add appropriate test coverage.

User interface changes

API changes

None - some implementations might no longer throw exceptions.

Data model changes

None

Release notes snippet