Enable flare without setting globals / patching onerror etc.

[jongbelegen]

I'm creating a widget and my code will be imported into many third-party websites.

I only want to report errors that are relevant to the "widget", also it's not good manners if my code sets globals on the window object.

Looking at the code I can achieve this currently by using https://github.com/facade/flare-client-js/blob/master/packages/client/src/FlareClient.ts directly with my API key.

This also means that I need to use a forked version of the vite plugin to upload sourcemaps that enables not setting globals.