Agora RTC Objective-C API Reference Refactor

### - f -

- FIT_MODE_COVER_POSITION : agora::rtc
- FIT_MODE_USE_IMAGE_RATIO : agora::rtc
- FORMAT_MP4 : agora::media
- FRAME_HEIGHT_540 : agora::rtc
- FRAME_RATE_FPS_1 : agora::rtc
- FRAME_RATE_FPS_10 : agora::rtc
- FRAME_RATE_FPS_15 : agora::rtc
- FRAME_RATE_FPS_24 : agora::rtc
- FRAME_RATE_FPS_30 : agora::rtc
- FRAME_RATE_FPS_60 : agora::rtc
- FRAME_RATE_FPS_7 : agora::rtc
- FRAME_WIDTH_960 : agora::rtc