Enable winit "default" feature

## What problem does this solve or what need does it fill?

I'm not sure why it was disabled in the first place. But enabling it brings Wayland by default, which fits in much better with my system, and is a more modern and potentially lower-latency/faster API.

## What solution would you like?

Enable winit "default" feature in bevy_winit.

## What alternative(s) have you considered?

If the intention was to have x11 as the default, at least add "winit/wayland-csd-adwaita" to bevy_winit's "wayland" feature, as without it, on desktops without SSD, the CSD looks pretty bad.