Eevee: Implement Overscan option

This option make the internal render size larger than the output size in
order to minimize screenspace effects disapearing at the render edges.

The overscan size added around the render is the maximum dimension
multiplied by the overscan percentage.

release/scripts/startup/bl_ui/properties_render.py

@@ -956,13 +956,21 @@ class RENDER_PT_eevee_film(RenderButtonsPanel, Panel):
         layout.use_property_split = True
 
         scene = context.scene
+        props = scene.eevee
         rd = scene.render
 
+        split = layout.split()
+        split.prop(props, "use_overscan")
+        row = split.row()
+        row.active = props.use_overscan
+        row.prop(props, "overscan_size", text="")
+
         col = layout.column()
         col.prop(rd, "filter_size")
         col.prop(rd, "alpha_mode", text="Alpha")
 
 
+
 class RENDER_PT_eevee_hair(RenderButtonsPanel, Panel):
     bl_label = "Hair"
     bl_options = {'DEFAULT_CLOSED'}