Plugins should not add code to sourcemap files

[beyerleinf]

Currently, sourcemap files also get modified by plugins, resulting in weird sourcemaps.

Example:

import __azf_shim_import_PATH from 'path';
import __azf_shim_import_URL from 'url'

const __dirname = __azf_shim_import_PATH.dirname(__azf_shim_import_URL.fileURLToPath(import.meta.url));
const __filename = __azf_shim_import_URL.fileURLToPath(import.meta.url);

import __azf_shim_import_MODULE from 'module';

const require = __azf_shim_import_MODULE.createRequire(import.meta.url);

{
  "version": 3,
  ...
}