This commit enables outputting non-linear convergence metrics, i.e.,
the MB and CNV values, per phase, for each non-linear iteration in
each timestep. If the user passes the option value "iterations" to
the --extra-convergence-output command line option, this commit will
create a new output file, CASE.INFOITER, that holds
* report step
* time step within that report step
* elapsed time
* MB and CNV values per phase
* well convergence status
for each non-linear iteration.
We use an asynchronous file writing procedure and confer ownership
of the report step's unprocessed convergence reports to this
procedure just before the end of
SimulatorFullyImplicitBlackoilEbos::runStep()
At that point, the convergence reports are about to go out of scope.
The asynchronous protocol uses a dedicated queue of output requests,
class ConvergenceReportQueue, into which the producer-i.e., member
function runStep()-inserts new convergence reports and from which
the output thread, ConvergenceOutputThread::writeASynchronous(),
retrieves those requests before writing the file data.
