fix:Dubbo3TripleGenerator use OuterClassName error

[xiaoyuuuuuupeng]

What is the purpose of the change

when option java_outer_classname is empty and use Dubbo3TripleGenerator generate code , the DubboxxxServiceTriple has error.
My proto file :

syntax="proto3";
option java_package="com.example.dubbo.proto";
option java_multiple_files=true;
service TestService {
  rpc echo(EchoReq)returns(EchoRes);
}

message EchoReq{
  string name = 1;
}

message EchoRes{
  string msg = 1;
}

and protoc-plugin

  <plugin>
                <groupId>org.xolstice.maven.plugins</groupId>
                <artifactId>protobuf-maven-plugin</artifactId>
                <version>0.6.1</version>
                <configuration>
                    <protocArtifact>com.google.protobuf:protoc:${protoc.version}:exe:${os.detected.classifier}</protocArtifact>
                    <pluginId>grpc-java</pluginId>
                    <protocPlugins>
                        <protocPlugin>
                            <id>dubbo</id>
                            <groupId>org.apache.dubbo</groupId>
                            <artifactId>dubbo-compiler</artifactId>
                            <version>3.0.10</version>
                            <mainClass>org.apache.dubbo.gen.tri.Dubbo3TripleGenerator</mainClass>
                        </protocPlugin>
                    </protocPlugins>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>test-compile</goal>
                            <goal>compile-custom</goal>
                            <goal>test-compile-custom</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

generated code DubboTestServiceTriple cannot find the TestServiceOuterClass

fixed: Dubbo3TripleGenerator use OuterClassName error

Brief changelog

1、change ProtoType util getJavaOuterClassname method from private to public
2、when option java_outer_classname is empty,serviceContext.outerClassName use ProtoType.getJavaOuterClassname method generate.

Verifying this change

Checklist

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c877d6e) 40.77% compared to head (f1d599c) 40.76%.

Additional details and impacted files

@@            Coverage Diff             @@
##              3.3   #13355      +/-   ##
==========================================
- Coverage   40.77%   40.76%   -0.01%     
==========================================
  Files        1805     1805              
  Lines       75644    75644              
  Branches    10617    10617              
==========================================
- Hits        30841    30839       -2     
- Misses      40487    40499      +12     
+ Partials     4316     4306      -10     

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