Sleep mode should give an indication when activated

[XLTechie]

Is your feature request related to a problem? Please describe.

Currently, when alt+tabbing to an application which has sleep mode active, NVDA gives no indication that sleep mode is being entered.
It speaks a fragment of what it would have spoken on normal switch to that window, realizes it should be in sleep mode, and goes silent.

This was brought to my attention by @marrie's comment in #3721. That feature, if implemented, will increase the need for an indication that sleep mode has been activated.

Describe the solution you'd like

A selector somewhere in settings that allows sleep mode to be indicated.
Options should be none, speech, or sound.

For sound, I or someone can produce an audio file containing a sound to indicate sleep mode.

It may be desirable, in conjunction with options resulting from #3721, to provide a Sleep mode settings panel.

[marrie]

I might add

• speach
• sound
• both
• braille
• none
  in case the user can't hear the sound, or the user needs or wants both a speach/braille and sound conformation.