[bugfix] Fix failure to look up remote profiles with duplicate emojis in some cases (#1534)

* Tidy up emoji parsing on profile submission

Don't bother reparsing for emoji unless one of the fields that can have
emoji in it has changed.
Deduplicate emoji between the display name and profile note - I'm not
sure whether this was hurting anything, but better safe.

* Deduplicate emoji when parsing remote accounts

Some servers - Misskey at least - don't deduplicate emoji, so it's
possible to get an account which has the same emoji used in both the
display name and note and therefore includes that emoji twice in its
metadata. When we start trying to put those into our database, we run
into a uniqueness constraint and fall over.

This change just deduplicates at the point of construction of an
account.

internal/ap/extract.go

@@ -453,6 +453,7 @@ func ExtractHashtag(i Hashtaggable) (*gtsmodel.Tag, error) {
 // ExtractEmojis returns a slice of emojis on the interface.
 func ExtractEmojis(i WithTag) ([]*gtsmodel.Emoji, error) {
 	emojis := []*gtsmodel.Emoji{}
+	emojiMap := make(map[string]*gtsmodel.Emoji)
 	tagsProp := i.GetActivityStreamsTag()
 	if tagsProp == nil {
 		return emojis, nil
@@ -477,6 +478,9 @@ func ExtractEmojis(i WithTag) ([]*gtsmodel.Emoji, error) {
 			continue
 		}
 
+		emojiMap[emoji.URI] = emoji
+	}
+	for _, emoji := range emojiMap {
 		emojis = append(emojis, emoji)
 	}
 	return emojis, nil