Add operation hashCode to OperationResult

[pgajek2]

Is your feature request related to a problem? Please describe.
operationId can be useful for debugging purpose.

Describe the solution you'd like
Add operationId to the OperationResult interface.

global interface OperationResult {
	// Metadata
	DML.OperationType operationType();
	Schema.SObjectType objectType();
        String operationId; // <==== operation hashCode
	Boolean hasFailures();
	// Errors
	List<Error> errors();
	// Records
	List<SObject> records();
	List<SObject> successes();
	List<SObject> failures();
	// Details
	List<RecordResult> recordResults();
}