[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/post-embeds/index.tsx

@@ -129,7 +129,9 @@ export function PostEmbeds({
               style={styles.singleImage}>
               {alt === '' ? null : (
                 <View style={styles.altContainer}>
-                  <Text style={styles.alt}>ALT</Text>
+                  <Text style={styles.alt} accessible={false}>
+                    ALT
+                  </Text>
                 </View>
               )}
             </AutoSizedImage>