Stop polluting the global namespace with fetch

[aaomidi]

ms-rest-js/lib/nodeFetchHttpClient.ts

Line 18 in 6244e91

const globalWithFetch = global as GlobalWithFetch;

As a self-contained library, doing this can cause havoc on other users. Lots of dual browser and node libraries check the global namespace for fetch before defaulting to requiring.

This code is essentially forcing its own flavor of node-fetch onto everything else that follows that same practice.

It shouldn't be necessary to pollute the global namespace like this.

[xirzec]

Seems like we could port Azure/azure-sdk-for-js#9880