Consider screen reader support when loader get focus

[kolaps33]

Bug Report

Steps

Navigate to example (loader is focusable with tabindex=0):
https://codesandbox.io/s/fluent-ui-example-q1gu7
Press TAB key until "loader" is focused

Expected Result

loader text is narrated

Actual Result

loader text is not narrated

Comment:
Currently VoiceOver narrae the content of the loader, but NVDA and JAWS not.
Based on the aria progress bar is not between the roles which should support the name taken from content:
https://www.w3.org/TR/wai-aria/#namefromcontent

Then author need to do labeling.
Aria recommend use aria-describedby:
https://www.w3.org/TR/wai-aria-1.1/#progressbar
but I would rather go with aria-labelledby point into the text element.