Replace ESM module with native ESM in assets build scripts

[Silic0nS0ldier]

UF managed NodeJS dependencies have all been refactored to use the native ESM support in NodeJS 12.17 onward. It is now time to switch to these, and remove the esm module entirely. This should provide a minor performance boost (no on-the-fly ES module compilation) but more importantly keep things running smoothly as more ES module packages appear on the NPM registry (the esm module is incompatible with native ESM support).