Consider umlaut forms when building tokenized map

Allows for writing broadcast player replacements using umlaut form (i.e
"Blübaum" instead of "Bluebaum") and have replacement happen even if the
name in the PGN is spelled "Bluebaum".

Previously each player replacement name was mapped into a single token
string which identifies the replacement info:
"Matthias Blübaum" -> Map("blubaum matthias" -> ReplacementInfo)

Now names with umlauts will make an additional mapping:
"Matthias Blübaum" -> Map("blubaum matthias"  -> ReplacementInfo,
                          "bluebaum matthias" -> ReplacementInfo)

Relates: lichess-org#15152

modules/relay/src/main/RelayPlayers.scala

@@ -42,7 +42,22 @@ private class RelayPlayersTextarea(val text: String):
 
   // With tokenized player names
   private lazy val tokenizedPlayers: Map[PlayerToken, RelayPlayer] =
-    players.mapKeys(name => tokenize(name.value))
+    players.iterator
+      .flatMap((name, player) => Set(name, umlautify(name)).map((_, player)))
+      .map((name, player) => (tokenize.apply(name.value), player))
+      .toMap
+
+  private def umlautify: PlayerName => PlayerName =
+    diacritics.iterator.foldLeft(_):
+      case (name, (k, v)) =>
+        if name.value.contains(k) then PlayerName(name.value.replaceAll(k, v)) else name
+
+  val diacritics = Map(
+    "ö" -> "oe",
+    "ä" -> "ae",
+    "ü" -> "ue",
+    "ß" -> "ss"
+  )
 
   // With player names combinations.
   // For example, if the tokenized player name is "A B C D", the combinations will be: