[typescript-fetch] Fix response type to be Response or undefined (#13825)

* Fix response type to be Response or undefined

Current generated code produces a `response` variable set to undefined, and TS does not like you changing the type of the variable later. Therefore, set the type of the variable to be `Response` or `undefined`

Solves OpenAPITools/openapi-generator#12007

* Update samples

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

@@ -166,7 +166,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/allOf-readonly/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

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

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/default/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/enum/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/es6-target/src/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/multiple-parameters/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/prefix-parameter-interfaces/src/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/sagas-and-records/src/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/with-interfaces/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/with-npm-version/src/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/with-string-enums/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {

samples/client/petstore/typescript-fetch/builds/without-runtime-checks/src/runtime.ts

@@ -177,7 +177,7 @@ export class BaseAPI {
                 }) || fetchParams;
             }
         }
-        let response = undefined;
+        let response: Response | undefined = undefined;
         try {
             response = await (this.configuration.fetchApi || fetch)(fetchParams.url, fetchParams.init);
         } catch (e) {