feat(editor): add --gen-texture-knit V-stitch fabric pattern

47th procedural texture: knit fabric V-stitch — each stitch
occupies a cellW x cellH cell holding the V-shape made by
two diagonal strokes meeting at the apex (cellW/2, 0) and
dropping to the cell's bottom corners. Cells tile contiguously
in both axes giving the iconic chevron-zigzag appearance of
knitted fabric stitches.

Useful for sweater fabric, woolly NPC clothing, blanket
textures, mitten/scarf set dressing, dwarven knitwork.
Defaults to 16x12 cells with 2-px stroke width.

tools/editor/cli_arg_required.cpp

@@ -81,6 +81,7 @@ const char* const kArgRequired[] = {
     "--gen-texture-lattice", "--gen-texture-honeycomb",
     "--gen-texture-cracked", "--gen-texture-runes",
     "--gen-texture-leopard", "--gen-texture-zebra",
+    "--gen-texture-knit",
     "--validate-glb", "--info-glb", "--info-glb-tree", "--info-glb-bytes",
     "--validate-jsondbc", "--check-glb-bounds", "--validate-stl",
     "--validate-png", "--validate-blp",