Support optimizers and preprocessor packages

-   Adds support for `preprocessorPackage`, which will be used for
    optimizers (mandatory) and translators (optional), to avoid
    entraining these dependencies in build products and to permit them
    to use Node.js overlays instead of browser overlays during the
    optimization process.
-   Reworks the flow of the loader:
    -   translate
    -   analyze dependencies
    -   optimize
    -   compile