This commit cleans up the code that manages remote rendering.
This fixes several issues: #15205, #17611, #18940, #18152, #18938,
and #18937. #17815 is also addressed since its no longer applicable.

ParaView no longer creates a single render window to use among all
vtkPVView instances on non-client processes like pvbatch or pvserver,
pvrenderserver. This shared render window was the root cause of several
headaches and necessitated classes like vtkPVSynchronizedRenderWindows
and extra burden on views to re-direct several calls like creating
windows, resizing windows to vtkPVSynchronizedRenderWindows. This is no
longer the case. Non-client processes still have a single viewable
window per proceses (vtkPVProcessWindow). However, this is not the
window that each view renders into. Instead, each view creates its own
vtkRenderWindow subclass. However, it's a FBO-based render window which
shares the context with the process specific render window
(created in vtkPVProcessWindow). This...