typescript-fetch: Properly detect and encode container request body param (OpenAPITools#3517)

Signed-off-by: Prateek Malhotra <someone1@gmail.com>
Co-Authored-By: Esteban Gehring <esteban.gehring@gmail.com>

Author: someone1

modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache

@@ -181,7 +181,7 @@ export class {{classname}} extends runtime.BaseAPI {
             {{#hasBodyParam}}
             {{#bodyParam}}
             {{#isContainer}}
-            body: requestParameters.{{paramName}}.map({{#items}}{{datatype}}{{/items}}ToJSON),
+            body: requestParameters.{{paramName}}{{#isListContainer}}{{#items}}{{^isPrimitiveType}}.map({{datatype}}ToJSON){{/isPrimitiveType}}{{/items}}{{/isListContainer}},
             {{/isContainer}}
             {{^isContainer}}
             {{^isPrimitiveType}}