plugin interaction helpers refactoring

src/mol-plugin/behavior/dynamic/camera.ts

src/mol-plugin/behavior/dynamic/representation.ts

...dynamic/selection/structure-representation-interaction.ts

src/mol-plugin/behavior/dynamic/volume-streaming/behavior.ts

src/mol-plugin/context.ts

src/mol-plugin/ui/viewport.tsx

src/mol-plugin/util/interaction.ts

src/mol-plugin/util/loci-label-manager.ts