function guessPackageName(requestedName) {
  const isNotPackageName =
    requestedName.startsWith('/') || requestedName.startsWith('.')
  if (isNotPackageName) {
    return
  }
  // resolving is skipped so guess package name
  const pathParts = requestedName.split('/')
  const nameSpaced = requestedName.startsWith('@')
  const packagePartCount = nameSpaced ? 2 : 1
  const packageName = pathParts.slice(0, packagePartCount).join('/')
  return packageName
}
For when you encounter a `requestedName` that was not inspected, likely
because resolution was skipped for that module

@type {ModuleToPackageFallbackFn}