Draw non-native art in .ai editing data from its PDF

A /ForeignObject (non-native art: the content of a placed PDF, which
Illustrator shows but doesn't edit) was left out with a note. The
letterhead of #861 keeps its fan of swooshes that way: a radial gradient
in a 3-point PDF, scaled 271 times and clipped by the swoosh paths, so
the page lost its main graphic.

The reader now decodes the object's ASCII85 /Data, has the PDF importer
read the PDF, and fits its art to the object's box as a group named
"Non-native art": /Bounds measured from /Origin with y down, then
/RTransform, which lands exactly on the clipping paths around both
objects of that file; the PDF's content is kept in its own y-up
coordinates, so it is flipped into the box. Ids are the document's and
the PDF's swatches stay unlinked; its images join the document by
content key. A PDF that can't be read is left out with a note, as
before.

The EPS crate now uses the PDF crate (same layer; allowed in the layer
check like render and metafile).

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ZwZjADUZP4VzvrFGpiZch

xtask/src/layers.rs

@@ -75,6 +75,8 @@ pub const INTRA_LAYER_ORDER: &[&[&str]] = &[
     &["text", "effects"],
     &["render", "eps"],
     &["metafile", "eps"],
+    // Non-native art in Illustrator editing data is a PDF, drawn by the PDF importer.
+    &["pdf", "eps"],
     &["plugins", "effects"],
 ];