[Video] Captions and alt text (#5009)

* video settings modal in composer

* show done button on web

* rm download options

* fix logic for showing settings button

* add language picker (wip)

* subtitle list with language select

* send captions & alt text with video when posting

* style "ensure you have selected a language" text

* include aspect ratio with video

* filter out captions where the lang is not set

* rm log

* fix label and add hint

* minor scrubber fix

src/view/com/composer/videos/VideoTranscodeBackdrop.web.tsx

@@ -1,7 +1,3 @@
-import React from 'react'
-
-export function VideoTranscodeBackdrop({uri}: {uri: string}) {
-  return (
-    <video src={uri} style={{flex: 1, filter: 'blur(10px)'}} muted autoPlay />
-  )
+export function VideoTranscodeBackdrop() {
+  return null
 }