fix: replace deprecated StatFs functions

`getAvailableBytes` is available since api 18
while current cordova-android must be >=12.0.0, so minSdk 24

src/android/DirectoryManager.java

@@ -84,9 +84,7 @@ public static long getFreeExternalStorageSpace() {
     public static long getFreeSpaceInBytes(String path) {
         try {
             StatFs stat = new StatFs(path);
-            long blockSize = stat.getBlockSize();
-            long availableBlocks = stat.getAvailableBlocks();
-            return availableBlocks * blockSize;
+            return stat.getAvailableBytes();
         } catch (IllegalArgumentException e) {
             // The path was invalid. Just return 0 free bytes.
             return 0;