when creating a new image.
We add a new function `gimp_metadata_set_creation_date` to
`libgimpbase/gimpmetadata` to handle setting all relevant
metadata tags.
We add a local function `gimp_image_new_add_creation_metadata` to
add the creation date metadata to relevant functions that create
new images.
We write tags for both the creation date and several modified dates
for IPTC, XMP and Exif metadata. All these use different ways to
express date/time and timezones and I can already see we need to have
another look at other places where we handle modified dates.
This solves the second part of #7287, adding metadata about the
date/time a new image was created.
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