* Allow rest/spread on polyfilled or builtin iterables when `Symbol` unsupported
Currently, when `Symbol` is not supported, we allow using rest/spread with:
- arrays
- strings
- arguments
With this PR, it will be also possible to use it with
- maps
- sets
- binary arrays
While in old browsers es6 builtins would still need to be polyfilled, it's way
easier to polyfill them because `Symbol` cannot be reliably polyfilled.
I didn't use `instanceof` becase:
- it doesn't work with polyfills not attatched to the global scope
- when using Babel to load polyfills, it would force the inclusion of `Map` and `Set` polyfills even if they are not used
Downside: the current approach of relying on `toString || construcor.name` doesn't work with subclasses.
* Don't use Array.from for array-like objects
* Node modules compatibility: add ".js" extension to imported polyfills
* Update fixtures
* add extensions on calling `addDefaultImport()`, not in the function.
