EEVEE: Motion Blur: Add shutter position option

This makes it easier to generate motion trail effect with EEVEE.

This just mimics the cycles option as described here:
https://docs.blender.org/manual/en/latest/render/cycles/render_settings/motion_blur.html

This fix T80070

release/scripts/startup/bl_ui/properties_render.py

@@ -173,7 +173,9 @@ class RENDER_PT_eevee_motion_blur(RenderButtonsPanel, Panel):
 
         layout.active = props.use_motion_blur
         col = layout.column()
+        col.prop(props, "motion_blur_position", text="Position")
         col.prop(props, "motion_blur_shutter")
+        col.separator()
         col.prop(props, "motion_blur_depth_scale")
         col.prop(props, "motion_blur_max")
         col.prop(props, "motion_blur_steps", text="Steps")