[C++][Compute] Promote Expression to the compute namespace

[asfimport]

See discussion in https://docs.google.com/document/d/1AyTdLU-RxA-Gsb9EsYnrQrmqPMOYMfPlWwxRi1Is1tQ

This will be necessary for ARROW-11928 since some ExecNodes will be constructed with one or more Expressions. For example FilterNodes will evaluate an Expression against their input batches to produce selection vectors.

This should probably include factoring out dataset-specific considerations such as allowing input batches diverge slightly in schema. Bound Expressions should refer to their parameters by index so that by-name lookup can be avoided.

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++] Implement array expression from R in C++ (is duplicated by)
• [Python] Enable calling compute functions on Expressions (is related to)
• [C++][Compute] Add Expression to type_fwd.h (is related to)

PRs and other links:

• GitHub Pull Request #10166

_{Note: This issue was originally created as ARROW-11929. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
Issue resolved by pull request 10166
#10166