disagg/subsets: factored out common part of distance-related extractors
disagg/subsets: factored out common part of distance-related extractors


Former-commit-id: 39fc53e22bdbb832b882b975fe0b799b64432459 [formerly 96f89d6c5f211eaf31ea386420f7282fd4bb3680]
Former-commit-id: 186b205971825ca39eb5d3ff1a397c2e36cdc49a
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine