Eevee: Refraction: Add "thickness" parameter.

This enables to fake a second refraction event. This is great to simulate thin planar objects such as glass panels.

release/scripts/startup/bl_ui/properties_material.py

@@ -1183,8 +1183,8 @@ class EEVEE_MATERIAL_PT_options(MaterialButtonsPanel, Panel):
         if mat.blend_method not in {"OPAQUE", "CLIP", "HASHED"}:
             layout.prop(mat, "transparent_hide_backside")
 
-        layout.prop(mat, "transparent_screen_refraction")
-
+        layout.prop(mat, "use_screen_refraction")
+        layout.prop(mat, "refraction_depth")
 
 
 classes = (