Event Loop 2.0 API and Windows implementation (#638)

* Rename EventsLoop and associated types to EventLoop

* Rename WindowEvent::Refresh to WindowEvent::Redraw

* Remove second thread from win32 backend

* Update run_forever to hijack thread

* Replace windows Mutex with parking_lot Mutex

* Implement new ControlFlow and associated events

* Add StartCause::Init support, timer example

* Add ability to send custom user events

* Fully invert windows control flow so win32 calls into winit's callback

* Add request_redraw

* Rename platform to platform_impl

* Rename os to platform, add Ext trait postfixes

* Add platform::desktop module with EventLoopExt::run_return

* Re-organize into module structure

* Improve documentation

* Small changes to examples

* Improve docs for run and run_return

* Change instances of "events_loop" to "event_loop"

* Rename MonitorId to MonitorHandle

* Add CHANGELOG entry

* Improve WaitUntil timer precision

* When SendEvent is called during event closure, buffer events

* Fix resize lag when waiting in some situations

* Update send test and errors that broke some examples/APIs

* Improve clarity/fix typos in docs

* Fix unreachable panic after setting ControlFlow to Poll during some RedrawRequested events.

* Fix crash when running in release mode

* Remove crossbeam dependency and make drop events work again

* Remove serde implementations from ControlFlow

* Fix 1.24.1 build

* Fix freeze when setting decorations

* Replace &EventLoop in callback with &EventLoopWindowTarget

* Document and implement Debug for EventLoopWindowTarget

* Fix some deadlocks that could occur when changing window state

* Fix thread executor not executing closure when called from non-loop thread

* Fix buffered events not getting dispatched

* Fix crash with runner refcell not getting dropped

* Address review feedback

* Fix CHANGELOG typo

* Catch panics in user callback

src/platform/ios.rs

@@ -0,0 +1,59 @@
+#![cfg(target_os = "ios")]
+
+use std::os::raw::c_void;
+
+use {MonitorHandle, Window, WindowBuilder};
+
+/// Additional methods on `Window` that are specific to iOS.
+pub trait WindowExtIOS {
+    /// Returns a pointer to the `UIWindow` that is used by this window.
+    ///
+    /// The pointer will become invalid when the `Window` is destroyed.
+    fn get_uiwindow(&self) -> *mut c_void;
+
+    /// Returns a pointer to the `UIView` that is used by this window.
+    ///
+    /// The pointer will become invalid when the `Window` is destroyed.
+    fn get_uiview(&self) -> *mut c_void;
+}
+
+impl WindowExtIOS for Window {
+    #[inline]
+    fn get_uiwindow(&self) -> *mut c_void {
+        self.window.get_uiwindow() as _
+    }
+
+    #[inline]
+    fn get_uiview(&self) -> *mut c_void {
+        self.window.get_uiview() as _
+    }
+}
+
+/// Additional methods on `WindowBuilder` that are specific to iOS.
+pub trait WindowBuilderExtIOS {
+    /// Sets the root view class used by the `Window`, otherwise a barebones `UIView` is provided.
+    ///
+    /// The class will be initialized by calling `[root_view initWithFrame:CGRect]`
+    fn with_root_view_class(self, root_view_class: *const c_void) -> WindowBuilder;
+}
+
+impl WindowBuilderExtIOS for WindowBuilder {
+    #[inline]
+    fn with_root_view_class(mut self, root_view_class: *const c_void) -> WindowBuilder {
+        self.platform_specific.root_view_class = unsafe { &*(root_view_class as *const _) };
+        self
+    }
+}
+
+/// Additional methods on `MonitorHandle` that are specific to iOS.
+pub trait MonitorHandleExtIOS {
+    /// Returns a pointer to the `UIScreen` that is used by this monitor.
+    fn get_uiscreen(&self) -> *mut c_void;
+}
+
+impl MonitorHandleExtIOS for MonitorHandle {
+    #[inline]
+    fn get_uiscreen(&self) -> *mut c_void {
+        self.inner.get_uiscreen() as _
+    }
+}