feat(modify): TXTEXP turns text into its character outlines

TXTEXP replaces each selected TEXT and MTEXT with one polyline per
glyph contour, on the text's layer and with its properties: a
lightweight polyline for flat text, a 3D polyline for tilted text.
The outlines come from the same glyph tessellation the text renders
with, so stroke fonts give their strokes and outline fonts their
closed contours.

Refs D#1665

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/modules/draw/modify/mod.rs

@@ -30,3 +30,4 @@ pub mod stretch;
 pub mod torient;
 pub mod translate;
 pub mod trim;
+pub mod txtexp;