Cross-browser compatibility issues with Fides-js

[eastandwestwind]

Bug Description

In testing https://github.com/ethyca/fides/issues/3319, it was discovered that older browsers (for example using Chrome 39 and Safari 10), had issues calling the fides-js route due to various syntax issues that differ by browser. Since these existed before, I kept the above ticket scoped to including fetch when needed, and opened this ticket to perform a fuller-scale evaluation of cross-browser support.

For this ticket, we need to:

1. Decide which browsers and versions we officially wish to support with fides-js cookie banner
2. Perform a fuller-scale evaluation of cross-browser support to determine which of our supported browsers are failing to load fides-js
3. Write follow-up tickets based on results to fix these issues.

Steps to Reproduce

1. Using Sauce Labs, navigate to http://localhost:3000/fides-js-demo.html using an old browser like Chrome 39 or Safari 10
2. Open console and see syntax issues that lead to fides-js API call failing

Here's an example screenshot using Safari 10:

Expected behavior

Fides-js should load and cookie banner should show.

[eastandwestwind]

Documenting here that @NevilleS suggests we support all evergreen browsers

[rsilvery]

@eastandwestwind did we ever resolve this? Thanks.