Another attempt to fix modifier keys behaviour

[last-partizan]

• Tested on all platforms changed
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

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This PR reverts https://github.com/maroider/winit/pull/1/files , not becouse it was bad or broken, but becouse i found real reason behind those strange modifiers behaviour, and maybe that PR fixed it, but it has added something to complexity.

Real reason: there was two places to track modifier states, and i removed one. There was three places to track modifiers (well, two in modifiers.rs and on in XkbState).

Maybe there was reason for this, which i don't know, but removing it simplified code and i used neovide with this change for a day, and not found any downsides.

Maybe this was stupid idea at all, but please take a look. And, maybe this changes should be combined with #1 instead of reverting, but i'll want you feedback before doing so.

[last-partizan]

This is updated version, where i found there is three places which are storing modiers. So, i removed utils/modifiers.rs, and are using ModifiersState::from_x11 where possible, and where impossible - i'm using from_xkb_modifiers.

[last-partizan]

Looks like it was already fixed by #6

Closing this.