[APP-724] Collection of accessibility fixes (#949)

* Fix: include alt text on the web lightbox image

* a11y: Dont read the 'ALT' label

* a11y: remove a wrapper behavior from posts

This appears to have been introduced with the goal of creating meta
actions on posts, but the behavior seems counter-productive. The
accessibility inspector was unable to access individual items within
the post and therefore most content was simply skipped.

There may be a way to support the post actions without losing the
ability to access the inner elements but I couldnt find it. -prf

* a11y: apply alt tags to image wrappers so they get read

* a11y: set Link accessibilityLabel to the title if none set

* a11y: skip the SANDBOX watermark

* a11y: improve post meta to not read UI and give a useful date

* ally: improve post controls

* a11y: add labels to lightbox images on mobile

* fix types

src/view/com/util/PostSandboxWarning.tsx

@@ -10,7 +10,10 @@ export function PostSandboxWarning() {
   if (store.session.isSandbox) {
     return (
       <View style={styles.container}>
-        <Text type="title-2xl" style={[pal.text, styles.text]}>
+        <Text
+          type="title-2xl"
+          style={[pal.text, styles.text]}
+          accessible={false}>
           SANDBOX
         </Text>
       </View>