Support `expr.IntervalYearToMonthLiteral` in `literalToDatum`

[benbellick]

arrow/compute/exprs.literalToDatum handles interval year/month literals through the *expr.ProtoLiteral path, but not the raw expr.IntervalYearToMonthLiteral type.

Let's add support for expr.IntervalYearToMonthLiteral.

Relevant code:

• literalToDatum type switch: https://github.com/apache/arrow-go/blob/v18.5.1/arrow/compute/exprs/exec.go#L182-L415
• Existing interval year/month handling in the *expr.ProtoLiteral path: https://github.com/apache/arrow-go/blob/v18.5.1/arrow/compute/exprs/exec.go#L355-L366
• expr.IntervalYearToMonthLiteral: https://github.com/substrait-io/substrait-go/blob/v7.5.0/expr/interval_year_to_month.go#L11-L68