Update ImageReaderSurfaceProducer.MAX_IMAGES to include the maximum number of retained dequeued images (flutter#174971)

MAX_IMAGES was set to 5 by
flutter/engine@7a58dac
in order to fix "client tried to acquire more than maxImages buffers"
warnings from ImageReader_JNI.


flutter@696251d
then converted lastDequeuedImage into a queue that retains up to
MAX_DEQUEUED_IMAGES in-flight images plus the latest dequeued image.
MAX_DEQUEUED_IMAGES was set to 2, but MAX_IMAGES was only incremented by
1. So the ImageReader_JNI warning may reappear in some cases.

This PR ensures that MAX_IMAGES provides enough capacity in the
ImageReader for the total number of images that may be in use.

Author: jason-simmons

engine/src/flutter/shell/platform/android/io/flutter/embedding/engine/renderer/FlutterRenderer.java

@@ -413,7 +413,6 @@ final class ImageReaderSurfaceProducer
           TextureRegistry.ImageConsumer,
           TextureRegistry.OnTrimMemoryListener {
     private static final String TAG = "ImageReaderSurfaceProducer";
-    private static final int MAX_IMAGES = 6;
     // The ImageReaderSurfaceProducer must not close images until the renderer,
     // either Skia OpenGL, Impeller OpenGL, or Impeller Vulkan is done reading
     // from them. The Vulkan renderer allows up to two frames in flight before
@@ -422,6 +421,7 @@ final class ImageReaderSurfaceProducer
     // the frame that references them has finished rendering can result in
     // tearing or other incorrect rendering.
     private static final int MAX_DEQUEUED_IMAGES = 2;
+    private static final int MAX_IMAGES = 5 + MAX_DEQUEUED_IMAGES;
 
     // Flip when debugging to see verbose logs.
     private static final boolean VERBOSE_LOGS = false;