expose ToRgba64 + add GetConfiguration to image frame

[UkooLabs]

was trying to do a copy of ImpageCompare code in ImageSharp.Textures however noticed ToRgba64 is internal and only ToVector4 is available, could you please make public...

Example use of ToRgba64

PixelOperations.Instance.ToRgba64(configuration, aSpan, aBuffer);

Additionally Image has a GetConfiguration() however there is no equivalent for ImageFrane