fun getResolutionUnit(resolution: int): double
Given the value from {@see #ExifTagKey.FOCAL_PLANE_RESOLUTION_UNIT} or {@see #ExifTagKey.RESOLUTION_UNIT} this method will return the corresponding value in millimeters
resolution - int: {@see #ExifTagKey.FOCAL_PLANE_RESOLUTION_UNIT} or {@see #ExifTagKey.RESOLUTION_UNIT}
Return
double: resolution in millimeters