[typescript] use const for middleware symbol (OpenAPITools#19478)

* style: use const for `middleware`

* chore: update generated code samples

Author: joscha

modules/openapi-generator/src/main/resources/typescript/types/ObservableAPI.mustache

@@ -66,14 +66,14 @@ export class Observable{{classname}} {
 
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
-        for (let middleware of this.configuration.middleware) {
+        for (const middleware of this.configuration.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
         return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
-                for (let middleware of this.configuration.middleware) {
+                for (const middleware of this.configuration.middleware) {
                     middlewarePostObservable = middlewarePostObservable.pipe(mergeMap((rsp: ResponseContext) => middleware.post(rsp)));
                 }
                 return middlewarePostObservable.pipe(map((rsp: ResponseContext) => this.responseProcessor.{{nickname}}WithHttpInfo(rsp)));

samples/client/others/typescript/builds/with-unique-items/types/ObservableAPI.ts

@@ -27,14 +27,14 @@ export class ObservableDefaultApi {
 
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
-        for (let middleware of this.configuration.middleware) {
+        for (const middleware of this.configuration.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
         return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
-                for (let middleware of this.configuration.middleware) {
+                for (const middleware of this.configuration.middleware) {
                     middlewarePostObservable = middlewarePostObservable.pipe(mergeMap((rsp: ResponseContext) => middleware.post(rsp)));
                 }
                 return middlewarePostObservable.pipe(map((rsp: ResponseContext) => this.responseProcessor.uniqueItemsWithHttpInfo(rsp)));

samples/openapi3/client/petstore/typescript/builds/browser/types/ObservableAPI.ts

@@ -34,14 +34,14 @@ export class ObservableDefaultApi {
 
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
-        for (let middleware of this.configuration.middleware) {
+        for (const middleware of this.configuration.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
         return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
-                for (let middleware of this.configuration.middleware) {
+                for (const middleware of this.configuration.middleware) {
                     middlewarePostObservable = middlewarePostObservable.pipe(mergeMap((rsp: ResponseContext) => middleware.post(rsp)));
                 }
                 return middlewarePostObservable.pipe(map((rsp: ResponseContext) => this.responseProcessor.filePostWithHttpInfo(rsp)));
@@ -63,14 +63,14 @@ export class ObservableDefaultApi {
 
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
-        for (let middleware of this.configuration.middleware) {
+        for (const middleware of this.configuration.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
         return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
-                for (let middleware of this.configuration.middleware) {
+                for (const middleware of this.configuration.middleware) {
                     middlewarePostObservable = middlewarePostObservable.pipe(mergeMap((rsp: ResponseContext) => middleware.post(rsp)));
                 }
                 return middlewarePostObservable.pipe(map((rsp: ResponseContext) => this.responseProcessor.petsFilteredPatchWithHttpInfo(rsp)));
@@ -92,14 +92,14 @@ export class ObservableDefaultApi {
 
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
-        for (let middleware of this.configuration.middleware) {
+        for (const middleware of this.configuration.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
         return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
-                for (let middleware of this.configuration.middleware) {
+                for (const middleware of this.configuration.middleware) {
                     middlewarePostObservable = middlewarePostObservable.pipe(mergeMap((rsp: ResponseContext) => middleware.post(rsp)));
                 }
                 return middlewarePostObservable.pipe(map((rsp: ResponseContext) => this.responseProcessor.petsPatchWithHttpInfo(rsp)));