android: jpeg: Configure thumbnailer based on request metadata

Configure the thumbnailer based on the thumbnail parameters given by the
android request metadata. Only the thumbnail encoder needs to be
configured, and since it is only used at post-processing time, move the
configuration out of the post-processor constructor and into the
processing step.

Also set the following android result metadata tags:
- ANDROID_JPEG_THUMBNAIL_SIZE
- ANDROID_JPEG_THUMBNAIL_QUALITY

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/android/jpeg/post_processor_jpeg.h

@@ -31,6 +31,7 @@ public:
 
 private:
 	void generateThumbnail(const libcamera::FrameBuffer &source,
+			       const libcamera::Size &targetSize,
 			       std::vector<unsigned char> *thumbnail);
 
 	CameraDevice *const cameraDevice_;