Dubbo cloud native (#4851)

* Polish #4542 : [Enhancement] Adapt the Java standard Event/Listener mechanism

* Polish #4541 : [Feature] Add local File System DynamicConfigurationFactory‘s extension

* Polish #4541 : Bugfix

* Polish #4541 : Optimization

* Polish #4541 : Add the compatibility for PollingWatchService on the some platforms

* Polish #4541 : Add delay publish without ThreadPoolExecutor

* Polish #4541 : Refactor the extension name

* Polish #4541 : Add remove ops

* Polish #4541 : Add testable constructor

* Polish #4541 : Add getConfigGroups method

* Polish #4610 : [Refactor] Refactor the bootstrap module

* Polish #4541 : Fix the nulling URL issue

* Polish #4622 : [Refactor] Refactor ConfigManager

* Polish #4622 : [Refactor] Refactor ConfigManager

* Polish #4622 : Support multiple configcenters

* Polish #4671 : ServiceNameMapping will not map the group, version and protocol

* update referenceCount log (#4683)

Add comments to support multiple shared connections

* Polish /#4687 : Remove the duplicated test code in dubbo-config-spring (#4688)

* #4685  修改代码if判断false问题 if (hasException == false)修改成if (!hasException) (#4695)

* Fixed Service annotation method parameters are not in effect (#4598)

* keep demo simple, and switch to use zookeeper as registry center (#4705)

* keep demo simple, and switch to use zookeeper as registry center

* remove comment

* @reference auto-wires the instance of generic interface #4594 (#4677)

* try to shorten maven output to make travis build pass (#4710)

* use CountDownLatch to check zk registry if establish connection (#4589)

* Minor change

* Rename the extension name of WritableMetadataService

* Polish #4759 : [Refactor] Change the signature of methods of MetadataService #4759

* Merge remote-tracking branch 'upstream/master' into dubbo-cloud-native

# Conflicts:
#	dubbo-all/pom.xml
#	dubbo-bom/pom.xml
#	dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/AbstractInterfaceConfig.java
#	dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/ApplicationConfig.java
#	dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/ConfigCenterConfig.java
#	dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/ReferenceConfig.java
#	dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/RegistryConfig.java
#	dubbo-config/dubbo-config-api/src/main/java/org/apache/dubbo/config/ServiceConfig.java
#	dubbo-config/dubbo-config-api/src/test/java/org/apache/dubbo/config/ReferenceConfigTest.java
#	dubbo-configcenter/dubbo-configcenter-api/src/main/java/org/apache/dubbo/configcenter/DynamicConfiguration.java
#	dubbo-configcenter/dubbo-configcenter-api/src/test/java/org/apache/dubbo/configcenter/mock/MockDynamicConfiguration.java
#	dubbo-configcenter/dubbo-configcenter-consul/src/main/java/org/apache/dubbo/configcenter/consul/ConsulDynamicConfiguration.java
#	dubbo-configcenter/dubbo-configcenter-etcd/src/test/java/org/apache/dubbo/configcenter/support/etcd/EtcdDynamicConfigurationTest.java
#	dubbo-configcenter/dubbo-configcenter-nacos/src/main/java/org/apache/dubbo/configcenter/support/nacos/NacosDynamicConfiguration.java
#	dubbo-configcenter/dubbo-configcenter-nacos/src/test/java/org/apache/dubbo/configcenter/support/nacos/NacosDynamicConfigurationTest.java
#	dubbo-configcenter/dubbo-configcenter-zookeeper/src/main/java/org/apache/dubbo/configcenter/support/zookeeper/ZookeeperDynamicConfiguration.java
#	dubbo-metadata/dubbo-metadata-api/src/main/java/org/apache/dubbo/metadata/definition/model/MethodDefinition.java
#	dubbo-metadata/dubbo-metadata-api/src/main/java/org/apache/dubbo/metadata/report/identifier/MetadataIdentifier.java
#	dubbo-metadata/dubbo-metadata-api/src/main/java/org/apache/dubbo/metadata/report/support/AbstractMetadataReport.java
#	dubbo-metadata/dubbo-metadata-api/src/test/java/org/apache/dubbo/metadata/report/identifier/MetadataIdentifierTest.java
#	dubbo-metadata/dubbo-metadata-definition-protobuf/src/main/java/org/apache/dubbo/metadata/definition/protobuf/ProtobufTypeBuilder.java
#	dubbo-metadata/dubbo-metadata-definition-protobuf/src/test/java/org/apache/dubbo/metadata/definition/protobuf/ProtobufTypeBuilderTest.java
#	dubbo-metadata/pom.xml
#	dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/integration/AbstractConfiguratorListener.java
#	dubbo-registry/dubbo-registry-nacos/src/main/java/org/apache/dubbo/registry/nacos/NacosRegistry.java
#	dubbo-registry/dubbo-registry-nacos/src/main/java/org/apache/dubbo/registry/nacos/NacosRegistryFactory.java
#	dubbo-rpc/dubbo-rpc-xml/src/main/java/org/apache/dubbo/xml/rpc/protocol/xmlrpc/XmlRpcProtocol.java

* Polish #3984 : Add the implementation of Page<ServiceInstance> getInstances(String serviceName, int offset, int pageSize, boolean healthyOnly)

* Code merge

* Fix the cases

* Merge remote-tracking branch 'upstream/cloud-native' into dubbo-cloud-native

# Conflicts:
#	dubbo-bootstrap/src/test/java/org/apache/dubbo/bootstrap/DubboServiceProviderBootstrap.java
#	dubbo-metadata/dubbo-metadata-definition-protobuf/pom.xml
#	dubbo-registry/dubbo-registry-api/src/test/java/org/apache/dubbo/registry/support/ServiceOrientedRegistryTest.java
#	dubbo-registry/dubbo-registry-consul/src/main/java/org/apache/dubbo/registry/consul/ConsulServiceDiscoveryFactory.java
#	dubbo-registry/dubbo-registry-etcd3/src/main/java/org/apache/dubbo/registry/etcd/EtcdServiceDiscovery.java

* Refactor ConfigManager

* Refactor ConfigManager

* Resolve the issues on ConfigManager

* Refactor and add test-cases for ConfigManager

* Polish #4774 : [Feature] Dubbo Cloud Native - To Support in Spring

* Polish #4808 : [Feature] Add the registered/unregistered event mechanism ShutdownHook

* Polish #4807 : [Feature] Add the callback mechanism ShutdownHook #4807

* Polish #4813 : [Feature] add Prioritized implementation for ServiceInstanceCustomizer

* Polish #4815 : [Feature] Add the ServiceLoader for Dubbo's services or components

* Polish #4815 : [Feature] Add the ServiceLoader for Dubbo's services or components

* Polish #4813 : [Feature] add Prioritized implementation for ServiceInstanceCustomizer

* Polish #4807 : Add sort implementation

* Refactor

* Refactor

* Polish #4845 : [Feature] Enhance the Event-Publishing feature to original ServiceDiscovery

* Merge remote-tracking branch 'upstream/cloud-native' into dubbo-cloud-native

# Conflicts:
#	dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/client/DefaultServiceDiscoveryFactory.java
#	dubbo-registry/dubbo-registry-api/src/main/java/org/apache/dubbo/registry/client/ServiceDiscoveryRegistry.java