Convert most of the Process class to Timeout<>

This changes most of the class to use the new Timeout class. The one function
left is RunThreadPlan, which I left for a separate change as the function is
massive. A couple of things to call out:
- I've renamed the affected functions to match the listener interface names. This
  should also help catch any places I did not convert at compile time.
- I've deleted the WaitForState function as it was unused.

llvm-svn: 288241