Improve emoji sticker suggestions.

There was a bug around some emoji being marked as 'obsolete' and
therefore not being found.

I also made a change so that you can use skin variations of emoji and
still find emoji tagged with the default yellow version of it.

Fixes #9471

app/src/main/java/org/thoughtcrime/securesms/components/emoji/EmojiUtil.java

@@ -0,0 +1,70 @@
+package org.thoughtcrime.securesms.components.emoji;
+
+import androidx.annotation.NonNull;
+
+import org.whispersystems.libsignal.util.Pair;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+public final class EmojiUtil {
+
+  private static final Map<String, String> VARIATION_MAP = new HashMap<>();
+
+  static {
+    for (EmojiPageModel page : EmojiPages.DATA_PAGES) {
+      for (Emoji emoji : page.getDisplayEmoji()) {
+        for (String variation : emoji.getVariations()) {
+          VARIATION_MAP.put(variation, emoji.getValue());
+        }
+      }
+    }
+  }
+
+  public static final int MAX_EMOJI_LENGTH;
+  static {
+    int max = 0;
+    for (EmojiPageModel page : EmojiPages.DATA_PAGES) {
+      for (String emoji : page.getEmoji()) {
+        max = Math.max(max, emoji.length());
+      }
+    }
+    MAX_EMOJI_LENGTH = max;
+  }
+
+  private EmojiUtil() {}
+
+  /**
+   * This will return all ways we know of expressing a singular emoji. This is to aid in search,
+   * where some platforms may send an emoji we've locally marked as 'obsolete'.
+   */
+  public static @NonNull Set<String> getAllRepresentations(@NonNull String emoji) {
+    Set<String> out = new HashSet<>();
+
+    out.add(emoji);
+
+    for (Pair<String, String> pair : EmojiPages.OBSOLETE) {
+      if (pair.first().equals(emoji)) {
+        out.add(pair.second());
+      } else if (pair.second().equals(emoji)) {
+        out.add(pair.first());
+      }
+    }
+
+    return out;
+  }
+
+  /**
+   * When provided an emoji that is a skin variation of another, this will return the default yellow
+   * version. This is to aid in search, so using a variation will still find all emojis tagged with
+   * the default version.
+   *
+   * If the emoji has no skin variations, this function will return the original emoji.
+   */
+  public static @NonNull String getCanonicalRepresentation(@NonNull String emoji) {
+    String canonical = VARIATION_MAP.get(emoji);
+    return canonical != null ? canonical : emoji;
+  }
+}