[C++][Compute] Add ExecNode hierarchy

[asfimport]

Per discussion on https://docs.google.com/document/d/1AyTdLU-RxA-Gsb9EsYnrQrmqPMOYMfPlWwxRi1Is1tQ

Add an ExecNode interface with which a streaming execution graph can be constructed. Initial concrete classes will include:

• ScanNode, which wraps a dataset and is a pure emitter of batches (initially, this will only wrap memory sized datasets such as tables. See ARROW-11930)
• FilterNode, which evaluates an expression on inputs and based on the result removes rows from batches (eventually, this may defer materialization of the selection to other kernels. See ARROW-5005 ARROW-10474)
• ProjectNode, which evaluates expressions on inputs producing new columns.
• GroupedAggregateNode, which computes aggregations grouped on one or more keys.

Reporter: Ben Kietzman / @bkietz
Assignee: Ben Kietzman / @bkietz

Related issues:

• [C++] C++ array kernels framework and execution buildout (umbrella issue) (is a child of)
• [C++] Query engine umbrella issue (is a child of)
• [C++] Implement LogicalPlan and LogicalPlanBuilder (supercedes)

PRs and other links:

• GitHub Pull Request #10204
• GitHub Pull Request #9742

_{Note: This issue was originally created as ARROW-11928. Please see the migration documentation for further details.}

[asfimport]

Ben Kietzman / @bkietz:
Issue resolved by pull request 10204
#10204