Bugfix #35920

Adding a new node in Node Editor failed for "High DPI" (Only Mac retina now).

- Py script for adding nodes was doing dpi magic, which it shouldn't. It has 
  been replaced with a (temporary) API call to set the correct cursor location.
  (Thanks to Lukas T for helping here)

- The SpaceNode->cursor[2] property now is *only* storing the coordinate
  in "adding new node space". Use of this has been removed from the code where
  possible, with as only exception the code to draw noodles while adding them.

Special coder note: Nodes should respect the DPI value, and draw larger with
larger buttons if you increase this size. The hack here is that this can only
work nice if also the node positions are scaled accordingly.

A better fix could be to check on scaling the node view itself for it. That
then would also remove this Python API call that was added in this commit.
However, that again might fight with how buttons layout code works now...
needs some careful checking.

release/scripts/startup/bl_operators/node.py

@@ -66,12 +66,8 @@ class NodeAddOperator():
 
         # convert mouse position to the View2D for later node placement
         if context.region.type == 'WINDOW':
-            # XXX, temp fix for [#35920], still fails for (U.pixelsize != 1)
-            dpi_fac = context.user_preferences.system.dpi / 72.0
-            space.cursor_location = v2d.region_to_view(event.mouse_region_x,
-                                                       event.mouse_region_y)
-            space.cursor_location /= dpi_fac
-
+            # convert mouse position to the View2D for later node placement
+            space.cursor_location_from_region(event.mouse_region_x, event.mouse_region_y) 
         else:
             space.cursor_location = tree.view_center