[video_player_videohole] Add get duration API for live stream

[xiaowei-guan]

Live stream duration is different from common video duration.

1. Live stream duration is a range, so we change duration variable from Duration to DurationRange, the DurationRange which include a start time and a end time.
2. The duration of the live stream changes during playback, so need add a timer to get duration.

[JSUYA]

https://github.com/flutter/packages/blob/main/packages/video_player/video_player_platform_interface/lib/video_player_platform_interface.dart#L229
Can't we just keep Duration type and use the value of duration.second returned by mediaplayer?
The interface that returns DurationRange for stream play seems to be buffered. (https://github.com/flutter/packages/blob/main/packages/video_player/video_player_platform_interface/lib/video_player_platform_interface.dart#L244)
what do you think?

[xiaowei-guan]

For live stream, the duration is a range which includes start time and end time.

 player_get_adaptive_streaming_info(player_, (void *)&live_duration_buff, PLAYER_ADAPTIVE_INFO_LIVE_DURATION);

When call seekTo, the time must be in the range， the start time is only used to judge. If remove start time, we might have seekTo issue.
I have tested seekTo for live stream, if we get live stream duration is [300, 500] and then call seekTo(200), the player just start with 300.

[JSUYA]

My worry is the change in interface. (I know, we have a separate interface from video_player_platform_interface.)

In my opinion..
When a user needs a seekTo point in valid range of streaming content, they can check the valid seekTo by taking the value from buffered rather than the duration value.
https://github.com/flutter/packages/blob/36a7b99381f85e86914e82c75fc7d9038ed96cca/packages/video_player/video_player_platform_interface/lib/video_player_platform_interface.dart#L241-L244

  /// Buffered parts of the video.
  ///
  /// Only used if [eventType] is [VideoEventType.bufferingUpdate].
  final List<DurationRange>? buffered;

Our int buffered is progress value of buffering. so we can change this API.
Of course, we don't necessarily have to follow the video_player_platform_interface, so this can be reconsidered later.