[video_player] Android: Added missing event.put("event", "completed");

[quentinleguennec]

Description

On Android a call to event.put("event", "completed"); is missing, which makes it impossible to know when the video is over. This fixes it.

Related Issues

None known.

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[quentinleguennec]

@mklim @bparrishMines Ready for review.

[iskakaushik]

@quentinleguennec, the change looks good. Once you address the merge conflicts we can land it.

[iskakaushik]

LGTM