We use `export default` begrudgingly here. Ideally we'd use just `export`, though this entire SDK expects things to be exported as a default. Instead of breaking everything, we'll sacrifice our export pattern for a smaller diff - a later commit can always do the default export -> regular export conversion.

This is needed because `require()` means something different in webpack - it ends up importing the module as something we didn't expect (and is occasionally async)

require() is a bit weird for riot-web's webpack, so we fork it out to its own function to reduce the weirdness. 

The added weirdness is that require() is sync though exports a module instead. If we use import(), we get a promise which doesn't help us here. We therefore have to require() and pull out the default export, though this is only a problem for webpack - babel (our chosen compiler for exporting ES6) doesn't need this, hence the if statement.

See element-hq/element-web@a1c9551

This is a similar fix to 18ac2db

Per matrix-org/matrix-js-sdk@f4d1c5c