SDK / exoplayer

It covers the following cases:

| From/To     | `null` | `surface 0` | `surface 1` |
|-------------|--------|-------------|-------------|
| `null`      | 🆖      | 📺           | 📺           |
| `surface 0` | ❌      | 🔁           | 📺           |
| `surface 1` | ❌      | 📺           | 🔁           |

Where
- 🆖 means NOP
- ❌ means
  - Set `null` on FrameProcessor, effectively dropping all frames
- 📺 means
  - Notify the listener of video size
  - Set FrameProcessor output surface and size when MSG_SET_VIDEO_OUTPUT_SIZE is received
- 🔁 means
  - Notify the listener of video size

PiperOrigin-RevId: 495477620