[JAVA] RxJava3 support

[tgerth]

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project beforehand.
• Run the shell script ./bin/generate-samples.shto update all Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/config/java*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

[wing328]

@tgerth thanks for the PR. Can you please remove the tabs with 4-space?

$ /bin/bash ./bin/utils/detect_tab_in_java_class.sh
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:		    LOGGER.warn("You specified all RxJava versions 1, 2 and 3 but they are mutually exclusive. Defaulting to v3.");
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:		    this.setUseRxJava3(Boolean.valueOf(additionalProperties.get(USE_RX_JAVA3).toString()));
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:		}else {
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:		    if (additionalProperties.containsKey(USE_RX_JAVA) && additionalProperties.containsKey(USE_RX_JAVA2)){
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:			    LOGGER.warn("You specified both RxJava versions 1 and 2 but they are mutually exclusive. Defaulting to v2.");
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:			    this.setUseRxJava2(Boolean.valueOf(additionalProperties.get(USE_RX_JAVA2).toString()));
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:		    }else if (additionalProperties.containsKey(USE_RX_JAVA) && additionalProperties.containsKey(USE_RX_JAVA3)) {
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:			    LOGGER.warn("You specified both RxJava versions 1 and 3 but they are mutually exclusive. Defaulting to v3.");
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        	    LOGGER.warn("You specified both RxJava versions 2 and 3 but they are mutually exclusive. Defaulting to v3.");
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        	    if(additionalProperties.containsKey(USE_RX_JAVA)){
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		    this.setUseRxJava(Boolean.valueOf(additionalProperties.get(USE_RX_JAVA).toString()));
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		}
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		if(additionalProperties.containsKey(USE_RX_JAVA2)){
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		    this.setUseRxJava2(Boolean.valueOf(additionalProperties.get(USE_RX_JAVA2).toString()));
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		}
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		if(additionalProperties.containsKey(USE_RX_JAVA3)){
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		    this.setUseRxJava3(Boolean.valueOf(additionalProperties.get(USE_RX_JAVA3).toString()));
modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java:        		}
Java files contain tab '\t'. Please remove it and try again.

[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[wing328]

Tested samples/client/petstore/java/retrofit2rx3 locally and the result is good. Will merge when all the CI tests pass

[wing328]

Will fix the outdated samples in a separate commit.

UPDATE: pushed f092b98