Draft: simplify import

refactoring code to make it simpler to read. A few fixes too.

There is a bug in Unity 2021.3.4f1 which prevents the asset processor from running, which means no libvlc binary gets properly configured, thus errors appear in the Unity Editor. This bug in Unity seems to be specific to the 2021 Unity Editor versions, the last few of which (which may include the bug fix, looking at their obscure release notes) are only available for download to Enterprise customers. We may just require our users to use Unity 2022+.