emoji [nfc]: Make a helper's helper not mutate lists of emoji names

We're about to change _generatePopularCandidates so it looks up the
emoji names in the ServerEmojiData, and we don't want to mutate
ServerEmojiData.

This isn't a hot codepath (it's called at most once per
server-emoji-data fetch), so creating a new List isn't a problem.

Author: chrisbobbe

lib/model/emoji.dart

@@ -216,11 +216,11 @@ class EmojiStoreImpl extends PerAccountStoreBase with EmojiStore {
 
   static List<EmojiCandidate> _generatePopularCandidates() {
     EmojiCandidate candidate(String emojiCode, List<String> names) {
-      final emojiName = names.removeAt(0);
+      final [emojiName, ...aliases] = names;
       final emojiUnicode = tryParseEmojiCodeToUnicode(emojiCode);
       assert(emojiUnicode != null);
       return EmojiCandidate(emojiType: ReactionType.unicodeEmoji,
-        emojiCode: emojiCode, emojiName: emojiName, aliases: names,
+        emojiCode: emojiCode, emojiName: emojiName, aliases: aliases,
         emojiDisplay: UnicodeEmojiDisplay(
           emojiName: emojiName, emojiUnicode: emojiUnicode!));
     }