drawShadowDepth

Renders this drawable's caster geometry into the currently bound cascade shadow map. Called once per cascade by DrawableShadow. The depth-pass program is already bound and the cascade's MVP base matrix loaded; the implementation only needs to bind its own vertex buffer, set its model translation via DrawableShadow.loadCasterTranslation / DrawableShadow.loadCasterMatrix, and call DrawableShadow.drawShapeStateOccluder (or issue raw draws for non-DrawShapeState geometry).