Envelopes: Anti-Alias and Preserve Shape Using change how distorted images draw

Envelope Options stored Anti-Alias and Preserve Shape Using, but nothing that
draws an image read them: a distorted image was always smoothed and always
cut into clip groups.

- With Anti-Alias off, each piece of a distorted image is marked pixelated
  (saved as `pixelated`). The renderer draws it with nearest-neighbor
  sampling and without mips, SVG export writes `image-rendering: pixelated`,
  and PDF export writes it without /Interpolate.
- With Preserve Shape Using Transparency, each piece is the image with a
  white opacity mask in the piece's shape instead of a clip group. The
  renderer paints an image whose mask is one plain white path straight into
  that path, as it does for an image in a clip group, when the path lies
  inside the image's frame.

Docs: docs/mcp.md, docs/target-app-parity.md.

crates/doc/src/node/extras.rs

@@ -23,6 +23,9 @@ pub struct NodeExtras {
     /// The group holds the glyph outlines of type. Geometry effects that reshape it move and scale
     /// the placed gradients in it with the outlines.
     pub type_outlines: bool,
+    /// An image drawn without smoothing: each pixel of the picture takes the color of the image
+    /// pixel nearest to it (an envelope's distorted image with Envelope Options › Anti-Alias off).
+    pub pixelated: bool,
     /// Editable Shaper composition; the original art is retained in its source child.
     pub shaper: Option<Box<crate::shaper::ShaperSpec>>,
     /// The [`crate::GraphicStyle::id`] last applied to this object. It stays linked while it keeps
@@ -56,6 +59,7 @@ pub(super) static NO_EXTRAS: NodeExtras = NodeExtras {
     graph: None,
     series_index: None,
     type_outlines: false,
+    pixelated: false,
     shaper: None,
     graphic_style: None,
     attrs: None,