[Dubbo-2499]fix PojoUtil realize type convert not support subclasses of 'java.util.date' #2499

[ningyu1]

What is the purpose of the change

fix PojoUtil realize type convert not support subclasses of 'java.util.date' #2499

Brief changelog

The type convert was modified to support the 'java.util.date' subclass

Verifying this change

org.apache.dubbo.common.utils.CompatibleTypeUtils.java
org.apache.dubbo.common.utils.PojoUtilsTest.java
org.apache.dubbo.common.utils.CompatibleTypeUtilsTest.java

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[diecui1202]

Looks good to me.

[diecui1202]

Need to merge back to 2.6.x?

[ningyu1]

@diecui1202 Yes ，I will send a pr that fixes the 2.6.x branch.

[ningyu1]

merge to 2.6.x #2502