android: Migrate from ndk-glue to ndk-context

`ndk-glue` suffers one fatal flaw: it's "only" supposed to be used by
the crate providing `fn main()` and only supposed to end up in the
dependency graph once as it has `static` globals which get duplicated
across versions.

In the current case with `winit 0.26` still on `ndk-glue 0.5` but
`cpal` on `ndk-glue 0.6` it'll always panic in `fn native_activity()` as
the `static` globals on this version is not initialized.

Introducing `ndk-context`: a crate that holds these `static`s, with the
intention/premise to not see a breaking release /ever/ and make this a
problem of the past.  The crate is currently initialized with the VM and
Android Context on `ndk-glue` 0.5.1 and 0.6.1 (0.4.1 pending) making it
compatible with whatever is current, and the possibility for backporting
to older `ndk-glue` versions too.

See also:
rust-mobile/ndk#211
rust-mobile/ndk#223

Cargo.toml

@@ -20,6 +20,9 @@ hound = "3.4"
 ringbuf = "0.2"
 clap = { version = "3", default-features = false, features = ["std"] }
 
+[target.'cfg(target_os = "android")'.dev-dependencies]
+ndk-glue = "0.6"
+
 [target.'cfg(target_os = "windows")'.dependencies]
 winapi = { version = "0.3", features = ["audiosessiontypes", "audioclient", "coml2api", "combaseapi", "debug", "devpkey", "handleapi", "ksmedia", "mmdeviceapi", "objbase", "profileapi", "std", "synchapi", "winbase", "winuser"] }
 asio-sys = { version = "0.2", path = "asio-sys", optional = true }
@@ -55,7 +58,7 @@ web-sys = { version = "0.3.35", features = [ "AudioContext", "AudioContextOption
 [target.'cfg(target_os = "android")'.dependencies]
 oboe = { version = "0.4", features = [ "java-interface" ] }
 ndk = "0.6"
-ndk-glue = "0.6"
+ndk-context = "0.1"
 jni = "0.19"
 
 [[example]]

src/host/oboe/android_media.rs

@@ -1,10 +1,9 @@
 use std::sync::Arc;
 
 extern crate jni;
-extern crate ndk_glue;
 
 use self::jni::Executor;
-use self::jni::{errors::Result as JResult, objects::JObject, JNIEnv, JavaVM};
+use self::jni::{errors::Result as JResult, JNIEnv, JavaVM};
 
 // constants from android.media.AudioFormat
 pub const ENCODING_PCM_16BIT: i32 = 2;
@@ -14,12 +13,11 @@ pub const CHANNEL_OUT_STEREO: i32 = 12;
 
 fn with_attached<F, R>(closure: F) -> JResult<R>
 where
-    F: FnOnce(&JNIEnv, JObject) -> JResult<R>,
+    F: FnOnce(&JNIEnv) -> JResult<R>,
 {
-    let activity = ndk_glue::native_activity();
-    let vm = Arc::new(unsafe { JavaVM::from_raw(activity.vm())? });
-    let activity = activity.activity();
-    Executor::new(vm).with_attached(|env| closure(env, activity.into()))
+    let android_context = ndk_context::android_context();
+    let vm = Arc::new(unsafe { JavaVM::from_raw(android_context.vm().cast())? });
+    Executor::new(vm).with_attached(|env| closure(env))
 }
 
 fn get_min_buffer_size(
@@ -31,7 +29,7 @@ fn get_min_buffer_size(
     // Unwrapping everything because these operations are not expected to fail
     // or throw exceptions. Android returns negative values for invalid parameters,
     // which is what we expect.
-    with_attached(|env, _activity| {
+    with_attached(|env| {
         let class = env.find_class(class).unwrap();
         env.call_static_method(
             class,