OpenAPI and Java Execution: Improve mapping inheritance and HttpAdapter support #136

- OpenAPI: Refine schema reference resolution to ensure type reuse and correct naming.
- OpenAPI: Integrate HttpJavaMappings and map typed requests/responses to HttpAdapter's HttpRequestData/HttpResponseData.
- Java Execution: Implement parent mapping delegation in MappingImpl to support inherited parameter mappings.
- Java Execution: Update JUnitTestGenerator to link subtype mappings to supertype mappings based on TDL extensions.