android: Minimal JNI for yuzu.

src/android/app/src/main/jni/id_cache.cpp

@@ -0,0 +1,36 @@
+#include "jni/id_cache.h"
+
+static JavaVM* s_java_vm;
+static jclass s_native_library_class;
+static jmethodID s_exit_emulation_activity;
+
+namespace IDCache {
+
+JNIEnv* GetEnvForThread() {
+    thread_local static struct OwnedEnv {
+        OwnedEnv() {
+            status = s_java_vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6);
+            if (status == JNI_EDETACHED)
+                s_java_vm->AttachCurrentThread(&env, nullptr);
+        }
+
+        ~OwnedEnv() {
+            if (status == JNI_EDETACHED)
+                s_java_vm->DetachCurrentThread();
+        }
+
+        int status;
+        JNIEnv* env = nullptr;
+    } owned;
+    return owned.env;
+}
+
+jclass GetNativeLibraryClass() {
+    return s_native_library_class;
+}
+
+jmethodID GetExitEmulationActivity() {
+    return s_exit_emulation_activity;
+}
+
+} // namespace IDCache