Always use shared: true and format: 'es'

[Rich-Harris]

There's no reason for shared: true to be configurable — there's no advantage in a webpack context to not sharing helpers.

I think the format should always be es — webpack can handle modules natively, right? (Not a webpack user, I could be wrong about this.) There's no reason for it to be anything else, is there?

More generally, rather than passing down each option in turn, it would probably make sense to pass through all the options, overriding the ones we need to.

[TheLarkInn]

Yup, so returned source can be esm export