Our XMP handling is spec-compliant while imagemagick's isn't

resize with negative values

Resizing jpg photo leads to raster artifacts

Imagemagick converts 16-bit PNGs to 8-bit but we don't

`-resize 10000x1000>` does not restrict size and creates huge image

Tests for the `wm-convert` binary

`null:` as a target file writes an actual file

`-identify` doesn't handle non-UTF-8 filenames

stripping metadata of a `jxl` image breaks the image

Allow disabling specific formats at compile time