Cycles/Eevee: unify depth of field settings for cameras

There is now a checkbox to enable/disable depth of field per camera. For Eevee
this replace the scene level setting. For Cycles there is now only an F-Stop
value, no longer a Radius.

Existing files are converted based on Cycles or Eevee being set in the scene.

Differential Revision: https://developer.blender.org/D4882

source/blender/python/gpu/gpu_py_offscreen.c

@@ -256,7 +256,6 @@ static PyObject *bpygpu_offscreen_draw_view3d(BPyGPUOffScreen *self,
                            false,
                            true,
                            "",
-                           NULL,
                            true,
                            self->ofs,
                            NULL);