Use UICommon's game list code on Android

Deduplicates code, and gets rid of some problems the old code had
(such as: bad performance when calling native functions, only one
disc showing up for multi-disc games, Wii banners being low-res,
unnecessarily much effort being needed for adding more metadata).

Source/Android/jni/AndroidCommon/AndroidCommon.cpp

@@ -0,0 +1,26 @@
+// Copyright 2018 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include "jni/AndroidCommon/AndroidCommon.h"
+
+#include <string>
+
+#include <jni.h>
+
+std::string GetJString(JNIEnv* env, jstring jstr)
+{
+  std::string result = "";
+  if (!jstr)
+    return result;
+
+  const char* s = env->GetStringUTFChars(jstr, nullptr);
+  result = s;
+  env->ReleaseStringUTFChars(jstr, s);
+  return result;
+}
+
+jstring ToJString(JNIEnv* env, const std::string& str)
+{
+  return env->NewStringUTF(str.c_str());
+}