fix for #11776 to correct handling of scalac -script target_script args

[philwalk]

The fix consists of this:

When -script target_script is first encountered, immediately transfer all remaining args to the script.
remove in_scripting_args

To verify the fix, I used these two scripts:
showargs.sc:

def main(args: Array[String]): Unit =
  for a <- args do
    println(s"[$a]")

hello.sc:

def main(args: Array[String]): Unit =
  println("hello!")

Command line to test for #11776:

$ scalac -script showargs.sc a b c -script hello.sc

Before the fix, the output would be:

$ hello!

With this fix, the output is:

[a]
[b]
[c]
[-script]
[hello.sc]