Since we're usually only providing `locateFile`, we need the type to be
`Partial<>` to allow it.
This also matches the typing in `@types/emscripten`'s
`EmscriptenModuleFactory` type signature.
This allows users to bail parsing if an error was *definitely* detected
using the progress callback, as all possible stack versions have a
non-zero error cost.
Co-authored-by: Amaan Qureshi <amaanq12@gmail.com>
