Add shadow options to image properties

[seekuehe]

This will allow us to export preset shadows on image blocks.
Required for #44359

[sam-pitch]

Running the following JS code in the sandbox produced the following presentation.

let pptx = new PptxGenJS();
let slide = pptx.addSlide();

slide.addImage({
  x: 1,
  y: 1,
  path: "https://images.unsplash.com/photo-1506744038136-46273834b3fb?crop=entropy&cs=tinysrgb&fit=max&fm=jpg&ixid=MnwyMTIyMnwwfDF8c2VhcmNofDJ8fGxhbmRzY2FwZXxlbnwwfHx8fDE2NTg5MzE0MDM&ixlib=rb-1.2.1&q=80&w=1080",
  shadow: {
    type: "outer",
    angle: 90,
    blur: 50,
    color: "FF0000",
    offset: 100,
    opacity: 0.5,
  },
});

pptx.writeFile({ fileName: "PptxGenJS-Sandbox.pptx" });

I will note that while I was writing in the sandbox I made some errors which caused the shadow to not render. (I didn't wrap the shadow props in a shadow object, and I put a # at the beginning of the color string) It's good that the presentation could still render but there wasn't any feedback I had fed it bad data.

[pastafari]

🎉

[seekuehe]

I added a validation in the correctShadowOptions function that will remove the extra # and send a warning on the console.