refactor android ffi

flutter/android/app/src/main/kotlin/ffi.kt

@@ -0,0 +1,19 @@
+// ffi.kt
+
+package ffi
+
+import android.content.Context
+import java.nio.ByteBuffer
+
+init {
+    System.loadLibrary("rustdesk")
+}
+
+external fun init(ctx: Context)
+external fun startServer(app_dir: String)
+external fun startService()
+external fun onVideoFrameUpdate(buf: ByteBuffer)
+external fun onAudioFrameUpdate(buf: ByteBuffer)
+external fun translateLocale(localeName: String, input: String): String
+external fun refreshScreen()
+external fun setFrameRawEnable(name: String, value: Boolean)