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GH-35506: [C++] Support First and Last aggregators in Substrait (#35513)

### Rationale for this change

See #35506

### What changes are included in this PR?

"first" and "last" are registered as aggregates in Substrait.

### Are these changes tested?

Yes, The test-cases cover grouped and non-grouped aggregation with "first" and "last", as well as "null" and non-"null" outputs.

### Are there any user-facing changes?

Yes, "first" and "last" will be valid in a consumed Substrait plan.
* Closes: #35506

Authored-by: Yaron Gvili <rtpsw@hotmail.com>
Signed-off-by: Li Jin <ice.xelloss@gmail.com>