Issues on Eclipse 2020-6 and 2018-12

[eriede]

I had issues with the debugger hanging @ 50% or so and giving no output. I downloaded the source and had a look. I found multiple problems.

1. SubProgressMonitor is deprecated and seems to have no effect.
   A drop in replacement is to change "new SubProgressMonitor(monitor, work)" to SubMonitor.convert(monitor, work). With this change, the status appeared in the progress bar.

2. HostShellProcessAdapter throws an IllegalThreadStateException if remoteShell has an IHostShellOutputListener already attached (as the code does).
   I changed the code to monitor the output of "remoteProcess.getInputStream()" instead. This appears to have fixed the issues. GDB now launches and I get output from the remote.

3. org.eclipse.cdt.dsf.gdb.internal.ui.launching.WorkingDirectoryBlock appears to be removed in 2020-06, (although the functionality still appears to work, even though an exception is thrown internally)
   After browsing the source for a bit, I found that the 2018-12 version still had this class. I debugged and applied the fixes using 2018-12, and then tested to see that 2020-06 worked as well.

Created PR #4 as a proposed fix.