Remove exception from sun.rmi.runtime.Log#getSource()

[Philippe Marschall]

Hello

First time contributor here.

We have exception tracing enabled in production and see thousands of
exceptions in sun.rmi.runtime.Log#getSource() to get the caller class.
In my option this should use StackWalker introduced in Java 9. I could
find no corresponding bug in JBS.

Attached you'll find a webrev. I created a custom StackWalker to be able
to pass in the estimated number of frames that we traverse. As for
variable naming conventions I tried to stick with other StackWalker
users I could find in the JDK. The stream formatting tries to follow the
LVTI style guidelines.

I have not written a test as the method is private. I ran the tier1
tests and they passed.

I have signed the OCA.

What are the next steps, where should I post this?

Cheers
Philippe Marschall