Deprecate window creation with stale event loop

Creating window when event loop is not running generally doesn't work,
since a bunch of events and sync OS requests can't be processed. This
is also an issue on e.g. Android, since window can't be created outside
event loop easily.

Thus deprecate the window creation when event loop is not running,
as well as other resource creation to running event loop.

Given that all the examples use the bad pattern of creating the window
when event loop is not running and also most example existence is
questionable, since they show single thing and the majority of their
code is window/event loop initialization, they wore merged into
a single example 'window.rs' example that showcases very simple
application using winit.

Fixes #3399.

src/platform_impl/macos/event_loop.rs

@@ -38,9 +38,7 @@ use super::{
 use crate::{
     error::EventLoopError,
     event::Event,
-    event_loop::{
-        ControlFlow, DeviceEvents, EventLoopClosed, EventLoopWindowTarget as RootWindowTarget,
-    },
+    event_loop::{ActiveEventLoop as RootWindowTarget, ControlFlow, DeviceEvents, EventLoopClosed},
     platform::{macos::ActivationPolicy, pump_events::PumpStatus},
 };
 
@@ -73,12 +71,12 @@ impl PanicInfo {
 }
 
 #[derive(Debug)]
-pub struct EventLoopWindowTarget {
+pub struct ActiveEventLoop {
     delegate: Id<ApplicationDelegate>,
     pub(super) mtm: MainThreadMarker,
 }
 
-impl EventLoopWindowTarget {
+impl ActiveEventLoop {
     #[inline]
     pub fn available_monitors(&self) -> VecDeque<MonitorHandle> {
         monitor::available_monitors()
@@ -134,7 +132,7 @@ impl EventLoopWindowTarget {
     }
 }
 
-impl EventLoopWindowTarget {
+impl ActiveEventLoop {
     pub(crate) fn hide_application(&self) {
         NSApplication::sharedApplication(self.mtm).hide(None)
     }
@@ -252,7 +250,7 @@ impl<T> EventLoop<T> {
             sender,
             receiver: Rc::new(receiver),
             window_target: Rc::new(RootWindowTarget {
-                p: EventLoopWindowTarget { delegate, mtm },
+                p: ActiveEventLoop { delegate, mtm },
                 _marker: PhantomData,
             }),
             panic_info,