Rollup tweaks for output size/perf

[developit]

This turns off externalLiveBindings, which generates getters for re-exported bindings.
It also enables modern code generation for the modern bundles (arrow functions, object shorthand, etc).

[changeset-bot]

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[quantizor]

@developit this change sounds good - picking it back up eventually?

[developit]

Yes - I think we are on more recent Rollup now too and can enable es2015 output.