[Java][Spring] fix RequestPart/RequestParam handling on multipart request (#14357)

Author: borsch

modules/openapi-generator/src/main/resources/JavaSpring/formParams.mustache

@@ -1 +1 @@
-{{#isFormParam}}{{^isFile}}{{>paramDoc}}{{#useBeanValidation}} @Valid{{/useBeanValidation}} @RequestParam(value = "{{baseName}}"{{#required}}, required = true{{/required}}{{^required}}, required = false{{/required}}){{>dateTimeParam}} {{{dataType}}} {{paramName}}{{/isFile}}{{#isFile}}{{>paramDoc}} @RequestPart(value = "{{baseName}}"{{#required}}, required = true{{/required}}{{^required}}, required = false{{/required}}) {{#isArray}}List<{{/isArray}}{{#reactive}}Flux<Part>{{/reactive}}{{^reactive}}MultipartFile{{/reactive}}{{#isArray}}>{{/isArray}} {{paramName}}{{/isFile}}{{/isFormParam}}
+{{#isFormParam}}{{^isFile}}{{>paramDoc}}{{#useBeanValidation}} @Valid{{/useBeanValidation}} {{#isModel}}@RequestPart{{/isModel}}{{^isModel}}@RequestParam{{/isModel}}(value = "{{baseName}}"{{#required}}, required = true{{/required}}{{^required}}, required = false{{/required}}){{>dateTimeParam}} {{{dataType}}} {{paramName}}{{/isFile}}{{#isFile}}{{>paramDoc}} @RequestPart(value = "{{baseName}}"{{#required}}, required = true{{/required}}{{^required}}, required = false{{/required}}) {{#isArray}}List<{{/isArray}}{{#reactive}}Flux<Part>{{/reactive}}{{^reactive}}MultipartFile{{/reactive}}{{#isArray}}>{{/isArray}} {{paramName}}{{/isFile}}{{/isFormParam}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java

@@ -608,7 +608,7 @@ public void testMultipartBoot() throws IOException {
                 .toParameter().toMethod()
                 .hasParameter("marker").withType("MultipartMixedRequestMarker")
                 .assertParameterAnnotations()
-                .containsWithNameAndAttributes("RequestParam", ImmutableMap.of("value", "\"marker\"", "required", "false"));
+                .containsWithNameAndAttributes("RequestPart", ImmutableMap.of("value", "\"marker\"", "required", "false"));
     }
 
     // Helper function, intended to reduce boilerplate