ui5-button: aria-expanded not working for screen reader

[SherrySherry123]

i am from Successfactors team, just find the aria-expanded attribute does not work for screen reader;

Describe the bug
ui5-button with aria-expanded=true/false is not read out by screen reader;

To reproduce
Steps to reproduce the behavior:

1. set aria-expanded=true for ui5-button
   <ui5-button aria-expanded="true">Enabled</ui5-button>
   2.While using any screen reader (JAWS, NVDA), tab over the button that has aria-expanded=true
   3."expanded/collapsed" never be read out

Expected behavior
when aria-expanded=true, a screen reader will announce "Expanded"
when aria-expanded=false, a screen reader will announce "Collapsed"

https://sap.github.io/ui5-webcomponents/playground/components/Button/