Start video playback in fullscreen landscape view by default

### Is your feature request related to a problem? Please describe.
I usually keep auto-rotation turned of on my Android phone, and lock it to a portrait orientation to prevent annoying accidental rotation if I'm reading in bed or holding my phone out to show someone something.

Currently, video playback in the Nextcloud app remains in portrait mode until I enable auto-rotate on my phone, then rotate my phone, and turn auto rotate back off when I'm done with the video.

Having to always use the three dot menu to make the video full screen is annoying too.

### Describe the solution you'd like
Apps from video streaming services like Netflix, Hulu, and Disney+ override the orientation lock and play videos in landscape orientation and full screen once a user taps play. The Nextcloud app should do the same.