fix(fetch): provide better @vercel/fetch encapsulation through the use of a static method on IsomorphicFetchHttpLibrary

Author: gfortaine

sdk-template-overrides/typescript/http/isomorphic-fetch.mustache

@@ -1,22 +1,24 @@
 import {HttpLibrary, RequestContext, ResponseContext} from './http{{extensionForDeno}}';
 import { from, Observable } from {{#useRxJS}}'rxjs'{{/useRxJS}}{{^useRxJS}}'../rxjsStub{{extensionForDeno}}'{{/useRxJS}};
-import createFetch, { FetchModule } from '@fortaine/fetch';
+import createFetch, { RequestInfo, RequestInit } from '@fortaine/fetch';
 {{#platforms}}
 {{#browser}}
 import "whatwg-fetch";
 {{/browser}}
 {{/platforms}}
 
-{{! https://github.com/ajaishankar/openapi-typescript-fetch#server-side-usage }}
-globalThis.fetch = createFetch(fetch as unknown as FetchModule) as any;
-
 export class IsomorphicFetchHttpLibrary implements HttpLibrary {
+    static fetch(...args: [RequestInfo, RequestInit]) {
+      const fetcher = {{#platforms}}{{#node}}(createFetch as any)(){{/node}}{{^node}}fetch{{/node}}{{/platforms}};
+
+      return fetcher(...args);
+    }
 
     public send(request: RequestContext): Observable<ResponseContext> {
         let method = request.getHttpMethod().toString();
         let body = request.getBody();
 
-        const resultPromise = fetch(request.getUrl(), {
+        const resultPromise = IsomorphicFetchHttpLibrary.fetch(request.getUrl(), {
             method: method,
             body: body as any,
             headers: request.getHeaders(),