v11: Active Effect retrieval

[bakbakbakbakbak]

The code has been marked in 4 places where it needs updating once @foundryvtt/foundryvtt#9185 has been decided and implemented into Core.

The code marking is looking like this:

	// @todo: V11 Compatability legacyTransferral
	//   Update to use the designed interface as specified here, once implemented into core
	//   https://github.com/foundryvtt/foundryvtt/issues/9185