Merge remote-tracking branch 'origin/master' into cte-nesting-support

Merge remote-tracking branch 'origin/master' into cte-nesting-support

* origin/master: (27 commits)
  reset key/name when TableValuedColumn is adapted
  limit None->null coercion to not occur with crud
  apply list() around weakkeydictionary iteration
  update case statement in dictlike-polymorphic
  Version 1.4.22 placeholder
  - 1.4.21
  Ensure alias traversal block works when adapt_from_selectables present
  typo
  changelog updates
  Adjust CTE recrusive col list to accommodate dupe col names
  Extract format_constraint truncation rules to ON CONFLICT
  labeling refactor
  Modernize tests - union
  implement independent CTEs
  Correct docs: pg8000 supports PostgreSQL UUID
  represent tablesample.sampling as FunctionElement in all cases
  repair schema_translate_map for schema type use cases
  implement deferred scalarobject history load
  add python 2.7 to pr workflow to help catch py3 only issues
  Docs: fixed typo in "Cascades"
  ...