BUG #15763: Fix mismatch in re-render state in client-server.
Avoid using camera's MTime to determine if the camera has changed. The rendering pipeline is fraught with calls that change the MTime when the camera may not have necessarily changed. That was causing the client/server to mismatch when deciding if the selection cache was to be cleared or not. Instead, we now simply use the mechanism already provided on the vtkSMRenderViewProxy side to clear cache forcibly when the camera sub-proxy is modified. This removes the dependence on camera's Mtime, as well as ensures that the cache is used for repeated selections when camera proxy isn't modified.