Reconcile argfile formats as much as possible between java and javac

Currently there are differences in @argfile features between the java and javac with jdk9.

Java for example allows for splitting a "run on line" using line escapes and eating white space added for readability. I found this to be very useful.

Per Jonathan, there are some issues that cannot be reconciled (like file encoding support).

It would be nice to reconcile as much as possible between the two tools however.

I filed this as a P3 because any consideration of this should be done before jdk 9 ships, as the java @argfile is new. Feel free to lower this if the work needs to be done in tbd_minor.

Jonathan said:
We can't address the file encoding issue, but the reality is, if you use UTF8, it will work for both java and javac.

We could look at translating the C code for the VM at-file support and consider using it in other tools, like javac, javadoc. Alternatively, we could make it a jdk API somewhere for common use by tools. (And yes, I know the VM couldn't use an API written in Java.)