dubbo:reference

在dubbo2.7.8中xml配置文件dubbo:reference不生效，以及ymal中没有dubbo.reference这个属性

Start by reproducing the report against Dubbo 2.7.8 with an XML dubbo:reference configuration and a YAML configuration, checking why the reference is not applied and why dubbo.reference is unavailable. Done means the reference configuration takes effect in both formats, with regression coverage for the reported cases.

Written by the indexing model from the issue text.