12.16 Documentation changes

12.16.1 New self-contained examples

These examples are entirely new:

(example-edit-file "capi/layouts/set-layout-ratios-keeping-fixed")

12.16.2 Removed self-contained examples

(example-edit-file "capi/graphics/image-access")
(example-edit-file "capi/graphics/image-access-bgra")