Move getxmp() to JpegImageFile

[radarhere]

Follow up to #5144

Moved getxmp() from Image to JpegImageFile, since the method fetches data from applist, which is a JpegImageFile property. Calling this method on a non-JPEG image would have caused an error.

[hugovk]

Thanks! I was going to add something like this to "API Additions" in the release notes, let's include it here?

Image.getxmp
^^^^^^^^^^^^

A new method has been added to return an object with tag names and values to make it
easier to find what you're looking for, instead of giving the tag number to
:py:meth:`~PIL.Image.Image.getexif`.

For example::

    >>> from PIL import Image
    >>> with Image.open("xmp_test.jpg") as im:
    >>>    print(im.getxmp())
    {'RDF': {}, 'Description': {'Version': '10.4', 'ProcessVersion': '10.0', 'ConvertToGrayscale': 'False', 'CameraProfile': 'Adobe Standard', 'LookTable': 'E1095149FDB39D7A057BAB208837E2E1'}, 'History': {}, 'Seq': {}, 'li': {}, 'DerivedFrom': {'documentID': '8367D410E636EA95B7DE7EBA1C43A412', 'originalDocumentID': '8367D410E636EA95B7DE7EBA1C43A412'}, 'ToneCurve': {}, 'ToneCurveRed': {}, 'ToneCurveGreen': {}, 'ToneCurveBlue': {}, 'ToneCurvePV2012': {}, 'ToneCurvePV2012Red': {}, 'ToneCurvePV2012Green': {}, 'ToneCurvePV2012Blue': {}, 'RetouchAreas': {}, 'Masks': {}, 'RetouchInfo': {}, 'Look': {}, 'Group': {}, 'Alt': {}, 'Parameters': {}}

[radarhere]

I've added release notes - it's different from your version though.

It isn't actually pulling data from getexif(). That was just being discussed as a reference for how the API should act.

>>> from PIL import Image
>>> im = Image.open("Tests/images/xmp_test.jpg")
>>> im.getxmp()
{'RDF': {}, 'Description': {'Version': '10.4', 'ProcessVersion': '10.0', 'ConvertToGrayscale': 'False', 'CameraProfile': 'Adobe Standard', 'LookTable': 'E1095149FDB39D7A057BAB208837E2E1'}, 'History': {}, 'Seq': {}, 'li': {}, 'DerivedFrom': {'documentID': '8367D410E636EA95B7DE7EBA1C43A412', 'originalDocumentID': '8367D410E636EA95B7DE7EBA1C43A412'}, 'ToneCurve': {}, 'ToneCurveRed': {}, 'ToneCurveGreen': {}, 'ToneCurveBlue': {}, 'ToneCurvePV2012': {}, 'ToneCurvePV2012Red': {}, 'ToneCurvePV2012Green': {}, 'ToneCurvePV2012Blue': {}, 'RetouchAreas': {}, 'Masks': {}, 'RetouchInfo': {}, 'Look': {}, 'Group': {}, 'Alt': {}, 'Parameters': {}}
>>> dict(im.getexif())
{296: 2, 34665: 222, 271: 'Canon', 272: 'Canon EOS Rebel T6', 305: 'Adobe Photoshop Lightroom Classic 7.4 (Macintosh)', 306: '2018:10:27 16:20:29', 282: 300.0, 283: 300.0}

In the last half hour, I've figured out what's going on, and I'm writing this partly for my future self.

If you look at https://en.wikipedia.org/wiki/Extensible_Metadata_Platform#Embedding, XMP data can be stored in multiple locations

JPEG – Application segment 1 (0xFFE1) with segment header "http://ns.adobe.com/xap/1.0/\x00"
...
PNG – inside an "iTXt" text block with the keyword "XML:com.adobe.xmp"

We do use "XML:com.adobe.xmp" internally elsewhere in Pillow at one point.

The code in this method is just for JPEG images though. We could make this method read data more generally in the future, but that is not for today.

[hugovk]

Great, thanks!