Android: rework backend to use android-activity crate (#2444)

This updates the Android backend to use the android-activity crate instead
of ndk-glue. This solves a few issues:
1. The backend is agnostic of the application's choice of Activity base
   class
2. Winit is no longer responsible for handling any Java synchronization
   details, since these are encapsulated by the design of
   android_activity
3. The backend no longer depends on global / static getters for state
   such as the native_window() which puts it in a better position to
   support running multiple activities within a single Android process.
4. Redraw requests are flagged, not queued, in a way that avoids taking
   priority over user events (resolves #2299)

To make it possible for application crates to avoid explicitly
depending on the `android-activity` crate (and avoid version conflicts)
this re-exports the android-activity crate under:

  `winit::platform::android::activity::*`

This also adds `android-native-activity` and `android-game-activity`
features that set the corresponding android-activity features.

Addresses: PR https://github.com/rust-windowing/winit/pull/1892
Addresses: PR https://github.com/rust-windowing/winit/pull/2307
Addresses: PR https://github.com/rust-windowing/winit/pull/2343

Addresses: #2293
Resolves: #2299

Co-authored-by: Markus Siglreithmaier <m.siglreith@gmail.com>

Co-authored-by: Markus Siglreithmaier <m.siglreith@gmail.com>

src/platform/android.rs

@@ -1,9 +1,9 @@
 use crate::{
-    event_loop::{EventLoop, EventLoopWindowTarget},
+    event_loop::{EventLoop, EventLoopBuilder, EventLoopWindowTarget},
     window::{Window, WindowBuilder},
 };
-use ndk::configuration::Configuration;
-use ndk_glue::Rect;
+
+use android_activity::{AndroidApp, ConfigurationRef, Rect};
 
 /// Additional methods on [`EventLoop`] that are specific to Android.
 pub trait EventLoopExtAndroid {}
@@ -17,7 +17,7 @@ pub trait EventLoopWindowTargetExtAndroid {}
 pub trait WindowExtAndroid {
     fn content_rect(&self) -> Rect;
 
-    fn config(&self) -> Configuration;
+    fn config(&self) -> ConfigurationRef;
 }
 
 impl WindowExtAndroid for Window {
@@ -25,7 +25,7 @@ impl WindowExtAndroid for Window {
         self.window.content_rect()
     }
 
-    fn config(&self) -> Configuration {
+    fn config(&self) -> ConfigurationRef {
         self.window.config()
     }
 }
@@ -36,3 +36,43 @@ impl<T> EventLoopWindowTargetExtAndroid for EventLoopWindowTarget<T> {}
 pub trait WindowBuilderExtAndroid {}
 
 impl WindowBuilderExtAndroid for WindowBuilder {}
+
+pub trait EventLoopBuilderExtAndroid {
+    /// Associates the `AndroidApp` that was passed to `android_main()` with the event loop
+    ///
+    /// This must be called on Android since the `AndroidApp` is not global state.
+    fn with_android_app(&mut self, app: AndroidApp) -> &mut Self;
+}
+
+impl<T> EventLoopBuilderExtAndroid for EventLoopBuilder<T> {
+    fn with_android_app(&mut self, app: AndroidApp) -> &mut Self {
+        self.platform_specific.android_app = Some(app);
+        self
+    }
+}
+
+/// Re-export of the `android_activity` API
+///
+/// Winit re-exports the `android_activity` API for convenience so that most
+/// applications can rely on the Winit crate to resolve the required version of
+/// `android_activity` and avoid any chance of a conflict between Winit and the
+/// application crate.
+///
+/// Unlike most libraries there can only be a single implementation
+/// of the `android_activity` glue crate linked with an application because
+/// it is responsible for the application's `android_main()` entry point.
+///
+/// Since Winit depends on a specific version of `android_activity` the simplest
+/// way to avoid creating a conflict is for applications to avoid explicitly
+/// depending on the `android_activity` crate, and instead consume the API that
+/// is re-exported by Winit.
+///
+/// For compatibility applications should then import the `AndroidApp` type for
+/// their `android_main(app: AndroidApp)` function like:
+/// ```rust
+/// #[cfg(target_os="android")]
+/// use winit::platform::android::activity::AndroidApp;
+/// ```
+pub mod activity {
+    pub use android_activity::*;
+}