Add example demonstrating how to correctly decode a stream of characters from winit

[alice-i-cecile]

          > I am still sort of baffled by the myriad of ways of getting a character from a winit key event, so I hope I'm doing this correctly.

I would love to see an example for this, but it probably shouldn't be this PR.

Originally posted by @alice-i-cecile in #11400 (comment)

[alice-i-cecile]

using ReceivedCharacter for whitespace doesn't work consistently cross-platform (winit bug)
combining ReceivedCharacter and KeyboardInput is buggy because there's no way to know which event came first
Which makes ReceivedCharacter useless, practically. Personally, I'm not sure why it even needs to exist. Definitely a discussion for another GitHub issue / PR though.

From @rparrett down the thread.