Revise Key and KeyCode enums

Split `Key` into clear categories, like `Named`, `Dead`, Character`, `Unidentified`
removing the `#[non_exhaustive]` from the `Key` itself.

Similar action was done for the `KeyCode`.

Fixes: #2995
Co-authored-by: Kirill Chibisov <contact@kchibisov.com>

examples/control_flow.rs

@@ -10,7 +10,7 @@ use simple_logger::SimpleLogger;
 use winit::{
     event::{ElementState, Event, KeyEvent, WindowEvent},
     event_loop::{ControlFlow, EventLoop},
-    keyboard::Key,
+    keyboard::{Key, NamedKey},
     window::WindowBuilder,
 };
 
@@ -88,7 +88,7 @@ fn main() -> Result<(), impl std::error::Error> {
                         request_redraw = !request_redraw;
                         println!("\nrequest_redraw: {request_redraw}\n");
                     }
-                    Key::Escape => {
+                    Key::Named(NamedKey::Escape) => {
                         close_requested = true;
                     }
                     _ => (),