ScanOptions currently has a number of constraints between members, which violates the contract of a public struct:

• filter must be bound to dataset_schema

• projection must be bound to dataset_schema

• projected_schema must be schema<...fields>, where the type of projection is struct<...fields>

  These are currently required to support FilterAndProjectScanTask, but after ARROW-13328 this complexity can be removed and ScanOptions can be a pure struct argument to MakeScanNode. Specifically, it should be possible to:

• remove the projected_schema field (ScanNode doesn't need to know the schemas of any subsequent nodes)

• remove the projection field (ScanNode doesn't need to know how or if scanned batches will be projected)

• provide a simple vector of FieldRef to indicate which fields should be materialized (MakeScanNode can validate that this includes every field referenced by filter)

• allow filter to be unbound (MakeScanNode can bind it to the dataset schema)

  dataset_schema seems slightly redundant too since MakeScanNode also takes a Dataset as an argument but it is currently used by CsvFileFormat to derive column types

Reporter: Ben Kietzman / @bkietz

Related issues:

• [C++][Dataset] Use an ExecPlan for synchronous scans or drop synchronous scans (depends upon)

_{Note: This issue was originally created as ARROW-13340. Please see the migration documentation for further details.}