[BUG] ui5-toast can not work on IE11

[Hubery-Shen]

Hi UI5 WebComponents team,

I am Hubery Shen from Successfactors. I are using ui5-toast component in UI5 Web Component Lib. And we found the fact that the ui5-toast component can not work on IE11.

Issue:
ui5-toast can not work on IE11

Expected:
ui5-toast can work on IE11

On Chrome:

On IE11:

You can repeat this bug through this website: ui5-toast on IE11