feat: implement SortByInternalDifficulty

SortByInternalDifficulty/MU3/patch_Scene_32_PrePlayMusic_MusicSelect.cs

@@ -0,0 +1,24 @@
+using MU3.DB;
+
+namespace MU3;
+
+public class patch_Scene_32_PrePlayMusic_MusicSelect: Scene_32_PrePlayMusic_MusicSelect {
+    private static patch_MusicSort1ID[] _sort1SettingList;
+    private extern void orig_Awake();
+
+    private void Awake() {
+        _sort1SettingList = new[] {
+            patch_MusicSort1ID.Genre,
+            patch_MusicSort1ID.All,
+            patch_MusicSort1ID.Character,
+            patch_MusicSort1ID.Version,
+            patch_MusicSort1ID.Level,
+            patch_MusicSort1ID.Name,
+            patch_MusicSort1ID.Attribute,
+            patch_MusicSort1ID.InternalLevel
+        };
+
+        orig_Awake();
+    }
+
+}

SortByInternalDifficulty/MU3/patch_UISortButton.cs

@@ -0,0 +1,27 @@
+using MU3.CustomUI;
+using UnityEngine;
+
+namespace MU3;
+
+class patch_UISortButton: UISortButton {
+    private MU3UIImageChanger _selectPreviewImageChanger;
+
+    protected override void Awake() {
+        base.Awake();
+
+        var changer = (patch_MU3UIImageChanger)_selectPreviewImageChanger;
+        var n = changer.sprites.Length;
+        var sprites = new Sprite[n + 1];
+
+        for(int i = 0; i < n; ++i) {
+            sprites[i] = changer.sprites[i];
+        }
+
+        Texture2D tex = new Texture2D(2, 2);
+        tex.LoadImage(InternalSortPreview.Bytes);
+
+        sprites[n] = Sprite.Create(tex, new Rect(0, 0, 254, 121), sprites[0].pivot);
+
+        changer.sprites = sprites;
+    }
+}