Add a scalar kernel is_inf that returns true at the positions of a floating point number array that have positive or negative infinite values (inf and -inf) and false at other positions. The implementation of this should be similar to is_nan. 

Reporter: Ian Cook / @ianmcook
Assignee: David Li / @lidavidm

Related issues:

• [C++] Arithmetic kernels for numeric arrays (is a child of)

PRs and other links:

• GitHub Pull Request #10375

_{Note: This issue was originally created as ARROW-12843. Please see the migration documentation for further details.}