split dssp calculation into multiple files

src/mol-model-props/computed/secondary-structure/dssp.ts

...rops/computed/secondary-structure/dssp/backbone-hbonds.ts

...ops/computed/secondary-structure/dssp/backbone-indices.ts

...ol-model-props/computed/secondary-structure/dssp/bends.ts

...-model-props/computed/secondary-structure/dssp/bridges.ts

...l-model-props/computed/secondary-structure/dssp/common.ts

...rops/computed/secondary-structure/dssp/dihedral-angles.ts

...-model-props/computed/secondary-structure/dssp/helices.ts

...-model-props/computed/secondary-structure/dssp/ladders.ts

...l-model-props/computed/secondary-structure/dssp/sheets.ts

...l-props/computed/secondary-structure/dssp/trace-lookup.ts

...ol-model-props/computed/secondary-structure/dssp/turns.ts