Use Alt text from image EXIF metadata if present

[stormwarning]

Describe the Feature

Now that more image tools* support the latest IPTC accessibility metadata properties it would be nice to reduce the friction in including alt-text by pulling the text from the image's metadata (if it exists).

*I don't have a comprehensive list, but I know Adobe Bridge and Adobe Lightroom support the -AltTextAccessibility tag.

The image's metadata could be checked when first added to the post composer and passed as an initial value to the alt text dialog so that it could still be modified if needed.

Attachments

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Describe Alternatives

I'm using exifreader to do this on my own site, but there could be similar libraries with a smaller bundle size that could work.

Additional Context

I'm happy to PR this change if it's something the team would like to add!