[adapters] 增加小游戏适配部分源码

adapters/platforms/xiaomi/wrapper/engine/download-ttf.js

@@ -0,0 +1,12 @@
+const downloader = cc.assetManager.downloader;
+const originalDownloadTTF = downloader._downloaders['.ttf'];
+
+function downloadTTF (url, options, onComplete) {
+    // can't use cached ttf on Xiaomi platform
+    options.cacheEnabled = false;
+    originalDownloadTTF(url, options, onComplete);
+}
+
+downloader.register({
+    '.ttf': downloadTTF,
+});

adapters/platforms/xiaomi/wrapper/engine/index.js

@@ -0,0 +1 @@
+require('./download-ttf');