Offer to use Alt Text from EXIF / metadata

[phlash]

As suggested by a fellow Mastadonian today: https://mastodon.social/@girlonthenet/110684069067869800

Android can already extract the required text via the ExifInterface API, either the TAG_USER_COMMENT or TAG_IMAGE_DESCRIPTION fields (priority given to User Comment as the later, more capable encoding, or simply merge them?)

My suggestion here is to offer any such strings as pre-populated Alt Text, retaining editing / replacement before posting?