Swatch libraries: Patterns › Geometric Patterns adds a pattern with its swatch

Window › Swatch Libraries and the Swatches panel's library menu get a
Patterns submenu with Geometric Patterns, a built-in library of eleven
black pattern swatches drawn in code (dots, stripes, a checkerboard, a
grid, diamonds, triangles, crosses and a zigzag).

- Clicking a pattern in its library panel adds the pattern and its
  swatch to the document and applies it to the active fill or stroke
  (Alt: the other one), as one undo step. A second click reuses the
  swatch; a different pattern under the same name keeps its name and
  the library's pattern comes in numbered.
- swatch.library.list lists the pattern libraries after the gradient
  libraries (category "patterns"), and swatch.library.add brings a
  pattern swatch's pattern as pasting art painted with it does.
- The library panel draws each pattern tile from the library's pattern.
- "Geometric Patterns" is translated in every catalog.

crates/engine/src/cmd.rs

@@ -62,6 +62,7 @@ pub mod params;
 mod path;
 pub(crate) mod pathops;
 mod patterncmds;
+pub mod patternlib;
 pub mod pdfcmds;
 pub mod perspgrid;
 pub mod place;