fix: added working bevy demo

[jmetz]

An option to fix the bevy template; this demo is a stripped down version of NiklasEi's
excellent bevy_game_tempalate.

Originally I created this: https://github.com/jmetz/cargo-mobile2-bevy-example/settings which serves as the basis for this template.

This is part of / addresses #379

Notes

• This is not the official breakout demo; that demo does not work well on android (no touch support, game viewport too wide).

[amrbashir]

Could you also update the templates/bevy template as it depends on templates/bevy-demo template and it is broken in this PR as well.

[jmetz]

Could you also update the templates/bevy template as it depends on templates/bevy-demo template and it is broken in this PR as well.

Done 👍

[amrbashir]

Thank you