nx_layout_block_horizontal_test.nx

nx_layout_block_horizontal_test.nx -- smoke for the Phase-3 horizontal margin/padding axis added to nx_layout_block in-place. Pairs with nx_layout_block_test (vertical-only) which still passes because new cascade lookups default to 0 when unspecified. Fixture (root + 1 child + 1 grandchild): root: padding-left: 10px padding-right: 5px (no margins, no width, no height) child: margin-left: 3px margin-right: 7px (no padding, no explicit width) grandchild: width: 50px (explicit) padding-left: 2px Expected geometry on viewport_w = 800: root.x = 0 + ml(0) = 0 root.w = avail(800) (no horizontal margins) root child_avail_w = 800 - pl(10) - pr(5) = 785 root content_origin_x = 0 + 10 = 10 child.x = content_origin_x(10) + ml(3) = 13 child.w = avail(785) - ml(3) - mr(7) = 775 child child_avail_w = 775 - pl(0) - pr(0) = 775 child content_origin_x = 13 + 0 = 13 grand.x = content_origin_x(13) + ml(0) = 13 grand.w = 50 (explicit) grand content_origin_x = 13 + pl(2) = 15