[BUG] On openapi-generator-maven-plugin v7.3.0 with interfaceOnly uses ApiUtil but does not generate it

Description

Upgrading from openapi-generator-maven-plugin v7.2.0 to v7.3.0.

Using configOptions like:

                <configOptions>
                  <!-- Whether to generate only API interface stubs without the server files -->
                  <interfaceOnly>true</interfaceOnly>
                  <!-- Generate code and provide dependencies for use with Spring Boot 3.x -->
                  <useSpringBoot3>true</useSpringBoot3>
                  <!-- Skip header parameters that matches given regex in the generated API methods
                  using @ApiImplicitParams annotation -->
                  <implicitHeadersRegex>prefer</implicitHeadersRegex>
                </configOptions>

The generated interface code now includes something like:

        getRequest().ifPresent(request -> {
            for (MediaType mediaType: MediaType.parseMediaTypes(request.getHeader("Accept"))) {
                if (mediaType.isCompatibleWith(MediaType.valueOf("application/problem+json"))) {
                    String exampleString = "Custom MIME type example not yet supported: application/problem+json";
                    ApiUtil.setExampleResponse(request, "application/problem+json", exampleString);
                    break;
                }
                if (mediaType.isCompatibleWith(MediaType.valueOf("application/problem+json"))) {
                    String exampleString = "Custom MIME type example not yet supported: application/problem+json";
                    ApiUtil.setExampleResponse(request, "application/problem+json", exampleString);
                    break;
                }
                if (mediaType.isCompatibleWith(MediaType.valueOf("application/problem+json"))) {
                    String exampleString = "Custom MIME type example not yet supported: application/problem+json";
                    ApiUtil.setExampleResponse(request, "application/problem+json", exampleString);
                    break;
                }
                if (mediaType.isCompatibleWith(MediaType.valueOf("application/problem+json"))) {
                    String exampleString = "Custom MIME type example not yet supported: application/problem+json";
                    ApiUtil.setExampleResponse(request, "application/problem+json", exampleString);
                    break;
                }
                if (mediaType.isCompatibleWith(MediaType.valueOf("application/problem+json"))) {
                    String exampleString = "Custom MIME type example not yet supported: application/problem+json";
                    ApiUtil.setExampleResponse(request, "application/problem+json", exampleString);
                    break;
                }
            }
        });
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);

But the ApiUtil class is not generated.

I tried adding following configuration properties without luck:

                <generateSupportingFiles>true</generateSupportingFiles>
                <supportingFilesToGenerate>ApiUtil.java</supportingFilesToGenerate>

With version v7.2.0 such java code is not generated (only the last return line is generated).

Start with the openapi-generator-maven-plugin handling of interfaceOnly and the generated Java interface shown in the report. Trace why that interface references ApiUtil while ApiUtil is absent, including whether supporting-file configuration is applied. Done means the interfaceOnly output is compilable and its behavior matches the v7.2.0 output or includes the required ApiUtil class.