add allowTransparentBackfaces parameter

CHANGELOG.md

src/mol-geo/geometry/cylinders/cylinders.ts

src/mol-geo/geometry/mesh/mesh.ts

src/mol-geo/geometry/spheres/spheres.ts

src/mol-geo/geometry/texture-mesh/texture-mesh.ts

src/mol-gl/shader/chunks/wboit-write.glsl.ts

src/mol-repr/util.ts