Fix explode query params for typescript-fetch (#22246)

Fixes: #10438

Author: Ivan-Roger

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

@@ -133,6 +133,17 @@ export class {{classname}} extends runtime.BaseAPI {
         {{/isArray}}
         {{^isArray}}
         if (requestParameters['{{paramName}}'] != null) {
+            {{#isExplode}}
+            {{#isContainer}}
+            for (let key of Object.keys(requestParameters['{{paramName}}'])) {
+                queryParameters[key] = requestParameters['{{paramName}}'][key];
+            }
+            {{/isContainer}}
+            {{^isContainer}}
+            queryParameters['{{baseName}}'] = requestParameters['{{paramName}}'];
+            {{/isContainer}}
+            {{/isExplode}}
+            {{^isExplode}}
             {{#isDateTimeType}}
             queryParameters['{{baseName}}'] = (requestParameters['{{paramName}}'] as any).toISOString();
             {{/isDateTimeType}}
@@ -144,6 +155,7 @@ export class {{classname}} extends runtime.BaseAPI {
             queryParameters['{{baseName}}'] = requestParameters['{{paramName}}'];
             {{/isDateType}}
             {{/isDateTimeType}}
+            {{/isExplode}}
         }
 
         {{/isArray}}

samples/client/petstore/typescript-fetch/builds/default-v3.0/apis/FakeApi.ts

@@ -1214,7 +1214,9 @@ export class FakeApi extends runtime.BaseAPI {
         }
 
         if (requestParameters['language'] != null) {
-            queryParameters['language'] = requestParameters['language'];
+            for (let key of Object.keys(requestParameters['language'])) {
+                queryParameters[key] = requestParameters['language'][key];
+            }
         }
 
         if (requestParameters['allowEmpty'] != null) {

samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/apis/FakeApi.ts

@@ -1072,7 +1072,9 @@ export class FakeApi extends runtime.BaseAPI {
         }
 
         if (requestParameters['language'] != null) {
-            queryParameters['language'] = requestParameters['language'];
+            for (let key of Object.keys(requestParameters['language'])) {
+                queryParameters[key] = requestParameters['language'][key];
+            }
         }
 
         if (requestParameters['allowEmpty'] != null) {