Feature Request: Custom save path

[NFSMONSTR]

It would be great to be able to specify a custom path for saving a file when saveAsFile is set to true

I made a quick and dirty patch based on a similar feature from VisionCamera, but unfortunately I'm not familiar enough with native development to make it good and clean:

vision-camera-cropper+1.3.1.patch

[xulihang]

This is a similar issue to this: #7