symtab initialization doesn't work with --auto-classpath

[NicolasRouquette]

I noticed a subtle problem in the argument validation logic,
At this time, I'm referring to this version: https://github.com/scalacenter/scalafix/blob/8bcc7d440b21bf05eda5cec37edcbe144c073701/scalafix-cli/src/main/scala/scalafix/internal/v1/Args.scala

Specifically, to the difference between:

• The logic of configuredSymtab, which uses the "raw" classpath:

  def configuredSymtab: Configured[SymbolTable] = {
    Try(
      ClasspathOps.newSymbolTable(
        classpath = classpath,
        out = out
      )
    ) match { ... }

• The logic of classLoader, which uses the "validated" classpath:

  def classLoader: ClassLoader =
    ClasspathOps.toOrphanClassLoader(validatedClasspath)

This means that when we use scalafix with --auto-classpath and [--auto-classpath-roots <dir>]* arguments, then the symbol table is effectively initialized with an empty classpath.

[olafurpg]

Fixed in #922