function getGPOS(lang, weight) {
  const pathInProject = `build-files/features/gpos-${lang.toLowerCase()}/${weight}.json`;
  if (!fs.existsSync(expandPath(pathInProject)))
    throw Error(`GPOS table ${pathInProject} is not found.`);
  return readJSON(pathInProject);
}
Get specified GPOS table
@param { 'J' | 'K' | 'SC' | 'TC' } lang 
@param { 'ExtraLight' | 'Light' | 'Normal' | 'Regular' | 'Medium' | 'Bold' 
| 'Heavy' } weight