Polyfill bigint

[nicktaras]

[SmartLayer]

I believe this is a draft PR because Nick mentioned he would try to not include polyfill here (but in Negotiator library instead, or the website repo).

[micwallace]

The usage of polyfills & node libraries is a bit of an issue. We can't expect websters to have to include these polyfills in their bundler configuration. I think we should start an effort to remove usage of node built-ins where possible and add any polyfills here for older browser support.

[micwallace]

No longer required as all modern browsers now support bigint