[#7755] assure deep copying of source job elements

- protect the values of input (parent, run) jobs when expanding a given job
- so that other jobs can use the same input jobs later with their values pristine
- (this is relevant when running multiple jobs with the same generator
  invocation)
- (and mostly affects map values)
(cherry picked from commit e058ff98042eb099d2340ab8ad038507b2c35e4d)