Android: Rewrite GetRenderSurfaceScale in Java

Long sequences of JNI calls are both hard to read and slow.

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/NativeLibrary.java

@@ -6,6 +6,7 @@
 
 package org.dolphinemu.dolphinemu;
 
+import android.util.DisplayMetrics;
 import android.view.Surface;
 
 import androidx.appcompat.app.AlertDialog;
@@ -571,5 +572,12 @@ public final class NativeLibrary
     }
   }
 
+  public static float getRenderSurfaceScale()
+  {
+    DisplayMetrics metrics = new DisplayMetrics();
+    sEmulationActivity.get().getWindowManager().getDefaultDisplay().getMetrics(metrics);
+    return metrics.scaledDensity;
+  }
+
   public static native float GetGameAspectRatio();
 }