In Image picker, the error from item provider was not surfaced. We should improve the code by surfacing the error to the dart public API so users can have more details about the errors when the picker failed.

This might also require public API updates where we can add a new error field to the PickedFile

See also: https://github.com/flutter/plugins/pull/4448/files#r755336904