add optional globals __dirname and __filename similar to node.js

[ivanitskiy]

add optional globals __dirname and __filename similar to node:

• https://nodejs.org/docs/latest/api/globals.html#__dirname
• https://nodejs.org/docs/latest/api/modules.html#__filename
  This may simplify locating files relative to source code (e.g. read/write some assets close to the loaded script).

Some node packages use these globals and thus may fail