[RUST-AXUM] fix generator not handling application/x-www-form-urlencoded request content (#18061)

* fix #18060

* isolate the option as separate flag

* apply modification suggested by @wing328

* remove added newlines

Author: denisbog

modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java

@@ -52,6 +52,7 @@
 import org.openapitools.codegen.config.GlobalSettings;
 import org.openapitools.codegen.examples.ExampleGenerator;
 import org.openapitools.codegen.languages.PhpNextgenClientCodegen;
+import org.openapitools.codegen.languages.RustAxumServerCodegen;
 import org.openapitools.codegen.languages.RustServerCodegen;
 import org.openapitools.codegen.meta.FeatureSet;
 import org.openapitools.codegen.meta.GeneratorMetadata;
@@ -4729,7 +4730,7 @@ public CodegenOperation fromOperation(String path,
             if (contentType != null) {
                 contentType = contentType.toLowerCase(Locale.ROOT);
             }
-            if (contentType != null &&
+            if (!(this instanceof RustAxumServerCodegen) && contentType != null &&
                     (contentType.startsWith("application/x-www-form-urlencoded") ||
                             contentType.startsWith("multipart"))) {
                 // process form parameters