Live Photo Support

Images sent using Element always gets converted to plain `.jpeg` files. Would be great to put support for Live Photos (as an option when sending) on the roadmap. Clients which does not support playback of the motion images, can convert it to a suitable format on device on-the-fly.

The issue names no file, test, or implementation entry point. Start by tracing Element iOS's image-sending flow and where images are converted to JPEG; define done as an optional Live Photo sending path with an appropriate fallback for clients that cannot play motion images.

Written by the indexing model from the issue text.