LocalVideoPreviewAttachment
A local preview stays attached until detach. Capture starts only after startCapture. Capture and call video-send state are separate; detach stops capture before removing the view.
actual class LocalVideoPreviewAttachment(owner: LocalVideoPreviewAttachmentOwner, val view: PlatformView)
A local preview stays attached until detach. Capture starts only after startCapture. Capture and call video-send state are separate; detach stops capture before removing the view.