Ensure that `Set` polyfill performance is acceptable

[craigkovatch]

From the ECMAScript spec:

Set objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structures used in this Set objects specification is only intended to describe the required observable semantics of Set objects. It is not intended to be a viable implementation model. https://tc39.es/ecma262/#sec-set-objects

Please verify that the polyfill for Set meets this performance requirement, similar to the work undertaken for Set in #219

[craigkovatch]

@JakeChampion as requested :) Hope this isn't too concise, I figured you have enough context but lmk if I need to add more background information here.

[craigkovatch]

@JakeChampion any update on this one? Was hoping it would be a quick fix after the fix in #219

[romainmenke]

Fixing this issue might also unblock Intl updates : https://github.com/Financial-Times/polyfill-library/pull/1186

see : https://github.com/formatjs/formatjs/issues/3747#issuecomment-1208354410