[Dubbo-6887] Fix the consumer accidentally using FixedThreadPool, resulting in threads starting with Dubbo-thread-xxx prefix

[tongxiao0622]

What is the purpose of the change

#6887

Brief changelog

There are many threads named with Dubbo-thread-xxx on the consumer side，these threads will not be recycled.
(中文：消费方出现了很多以Dubbo-thread-xxx命名的线程，这些线程不会被回收)

Verifying this change

消费方感知到提供方下线或者禁用

AllChannelHandler#disconnected -> getExecutorService() -> getSharedExecutorService()
-> DefaultExecutorRepository#getExecutor -> 此时消费方关联线程池已关闭(executor.isShutdown() || executor.isTerminated()) -> createExecutor(url)

上面的URL并不存在threadname、threadpool参数，导致消费方创建了FixedThreadPool线程池

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[AlbumenJ]

@tongxiao0622 Hi, thanks for your contribution.

Please merge the latest master to resolve confilcts.

[AlbumenJ]

Close for long time no response.

Please feel free to reopen if you have any question.

If you think these changes still useful in the latest master branch, please submit a new pull request.