depth render pass, clear related fixes

src/mol-canvas3d/canvas3d.ts

src/mol-canvas3d/helper/postprocessing.ts

src/mol-gl/compute/util.ts

src/mol-gl/renderer.ts

src/mol-gl/shader/chunks/assign-material-color.glsl.ts

src/mol-gl/shader/chunks/common.glsl.ts

src/mol-gl/shader/direct-volume.frag.ts

src/mol-gl/shader/lines.frag.ts

src/mol-gl/shader/mesh.frag.ts

src/mol-gl/shader/points.frag.ts

src/mol-gl/shader/postprocessing.frag.ts

src/mol-gl/shader/spheres.frag.ts

src/mol-gl/shader/text.frag.ts

src/mol-gl/webgl/extensions.ts

src/mol-gl/webgl/render-item.ts

src/mol-math/geometry/gaussian-density/gpu.ts