fixes to DSSP impl, detection of bends and sheets

src/mol-math/linear-algebra/3d/vec3.ts

src/mol-math/linear-algebra/_spec/vec3.spec.ts

...ol-model/structure/model/properties/seconday-structure.ts

...l/structure/model/properties/utils/secondary-structure.ts

...ure/model/properties/utils/secondary-structure.validation

src/mol-model/structure/model/types.ts

src/mol-theme/color/secondary-structure.ts

src/tests/browser/render-structure.ts