Multi-view: per-cell stats in the corner (resolution, codec, decoded/received fps) #82

Measure how much the hardware decoder really handles, instead of guessing from the declared limits.

Each multi-view cell shows small text in a corner, updated once per second:

1920×1080 H.264 25/25 fps

• resolution and codec: from the decoder's output format;
• received fps: complete frames that arrived (RTP marker bit on video);
• decoded fps: frames the decoder returned and rendered.

When decoded < received, the decoder is not keeping up; this is the real per-device limit. The same numbers go to logcat every few seconds (Quad-N: … fps) for device reports.

Context: on the AG-216 the declared H.264/H.265 budget is 489 600 macroblocks/s (= 1080p60 in total), but 8 streams of 1080p20–25 (about 2.5–3× that) played without decoder errors in #74. Only a per-cell measurement shows whether every frame was shown. Related: #80, #76.