`__pdfjsdev_webpack__` was used to skip evaluating part of an AST,
in order to not mangle some `require` symbols.
This commit removes `__pdfjsdev_webpack__`, and:
- Uses `__non_webpack_require__` when one wants the output to
contain `require` instead of `__webpack_require__`.
- Adds options to the webpack config to prevent "polyfills" for
some Node.js-specific APIs to be added.
- Use `// eslint-disable-next-line no-undef` instead of `/* globals ... */`
for variables that are not meant to be used globally.
