rendering: preserve raster and pixel-text semantics in DrawList

[tritao]

Purpose

Preserve retained raster and screen-space image/text semantics on top of the material/lighting layer and the shared SoText2 preparation foundation.

Includes

• semantic wide-line handling, including native-range fallback, line-strip continuity, full line-pattern masks, and correct geometry-shader dispatch;
• semantic point-size handling, including native-range fallback and triangle wireframe/point-mode dispatch;
• retained visibility, winding, culling, polygon-offset targets, and viewport-local raster state;
• retained SoImage screen-space image rasterization;
• shared retained SoText2 pixel rasterization from CPU glyph generation through the core-profile textured draw path;
• pixel-origin and viewport-sized shader modes required by image and pixel-text rendering.

Deliberately excluded

Material/light state capture, text layout/glyph preparation, picking/selection, and render-layer/context orchestration.

Review question

Do retained lines, points, images, and pixel text preserve Coin raster semantics without introducing profile-specific legacy behavior?

Stack

Layer 15/18, based on PR #57.