补充文件缓存预加载接口prefetchToFileCache,以及ImageKnifeOption属性isCacheable、onlyRetrieveFromCache

Signed-off-by: zgf8268 <zenggaofeng2@h-partners.com>

entry/src/main/ets/pages/TestPrefetchToFileCache.ets

@@ -23,7 +23,7 @@ struct TestPrefetchToFileCachePage {
   }
   async preload(url:string) {
     let fileCachePath = await ImageKnife.getInstance().prefetchToFileCache(url)
-    console.log("文件缓存的路径是："+ fileCachePath)
+    console.log("preload-fileCachePath=="+ fileCachePath)
   }
   build() {
     Column() {