This PR introduces the ability to save videos to custom locations, taking into account the limitations and behavior of each platform.

Due to platform-specific security restrictions and limitations:

* On Android, I was able to save videos directly to `/storage/emulated/0/Download/video.mp4` without issues.
* On iOS, I was able to save videos to `On My iPhone -> Camera Example -> Movies`.
* On Windows, the behavior is similar to Android.

Closes https://github.com/flutter/flutter/issues/91680

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