Depsgraph: remove EvaluationContext, pass Depsgraph instead.

The depsgraph was always created within a fixed evaluation context. Passing
both risks the depsgraph and evaluation context not matching, and it
complicates the Python API where we'd have to expose both which is not so
easy to understand.

This also removes the global evaluation context in main, which assumed there
to be a single active scene and view layer.

Differential Revision: https://developer.blender.org/D3152

source/blender/python/intern/gpu_offscreen.c

@@ -163,7 +163,7 @@ PyDoc_STRVAR(pygpu_offscreen_draw_view3d_doc,
 );
 static PyObject *pygpu_offscreen_draw_view3d(BPy_GPUOffScreen *self, PyObject *args, PyObject *kwds)
 {
-	/* TODO: This doesn't work currently because of eval_ctx. */
+	/* TODO: This doesn't work currently because of missing depsgraph. */
 #if 0
 	static const char *kwlist[] = {"scene", "view_layer", "view3d", "region", "projection_matrix", "modelview_matrix", NULL};