EEVEE-Next: Shadows: Add global switch

This allow to bypass all cost associated with shadow mapping.

This can be useful in certain situation, such as opening a scene on a
lower end system or just to gain performance in some situation (lookdev).

release/scripts/startup/bl_ui/properties_render.py

@@ -469,6 +469,11 @@ class RENDER_PT_eevee_next_shadows(RenderButtonsPanel, Panel):
     def poll(cls, context):
         return (context.engine in cls.COMPAT_ENGINES)
 
+    def draw_header(self, context):
+        scene = context.scene
+        props = scene.eevee
+        self.layout.prop(props, "use_shadows", text="")
+
     def draw(self, context):
         layout = self.layout
         layout.use_property_split = True