emoji [nfc]: Drop setServerEmojiData from main interface

Instead, leave it as a method on EmojiStoreImpl and on the overall
PerAccountStore.

Each of these FooStore types, such as EmojiStore, is implemented by
both a FooStoreImpl class and the overall PerAccountStore.  Nearly all
of these types' methods behave exactly the same on both those types;
the one implementation just forwards to the other.

But this method behaves slightly differently between them: the
PerAccountStore implementation will call notifyListeners, while the
EmojiStoreImpl implementation doesn't (because it can't, not being the
ChangeNotifier itself).

That mismatch, when nearly all the other similar methods have an
exact match, risks confusion.  Mitigate that by removing the method
from the EmojiStore interface, so that the two implementations become
unrelated methods.

(The one other such mismatch is `reconcileMessages`.  We'll deal
with that one too, in a later commit.)

Author: gnprice

lib/model/emoji.dart

@@ -122,8 +122,6 @@ mixin EmojiStore {
   // TODO cut debugServerEmojiData once we can query for lists of emoji;
   //   have tests make those queries end-to-end
   Map<String, List<String>>? get debugServerEmojiData;
-
-  void setServerEmojiData(ServerEmojiData data);
 }
 
 /// The implementation of [EmojiStore] that does the work.
@@ -374,7 +372,6 @@ class EmojiStoreImpl extends PerAccountStoreBase with EmojiStore {
     return _allEmojiCandidates ??= _generateAllCandidates();
   }
 
-  @override
   void setServerEmojiData(ServerEmojiData data) {
     _serverEmojiData = data.codeToNames;
     _popularCandidates = null;

lib/model/store.dart

@@ -587,18 +587,17 @@ class PerAccountStore extends PerAccountStoreBase with
   @override
   Map<String, List<String>>? get debugServerEmojiData => _emoji.debugServerEmojiData;
 
-  @override
-  void setServerEmojiData(ServerEmojiData data) {
-    _emoji.setServerEmojiData(data);
-    notifyListeners();
-  }
-
   @override
   Iterable<EmojiCandidate> popularEmojiCandidates() => _emoji.popularEmojiCandidates();
 
   @override
   Iterable<EmojiCandidate> allEmojiCandidates() => _emoji.allEmojiCandidates();
 
+  void setServerEmojiData(ServerEmojiData data) {
+    _emoji.setServerEmojiData(data);
+    notifyListeners();
+  }
+
   EmojiStoreImpl _emoji;
 
   //|//////////////////////////////