[C++][Compute] Add explicit output values to sign function and fix unary type checks

[asfimport]

The sign function implementation for unsigned integers returns the result of a boolean expression because when casted to an integer it corresponds to the expected value (0 or 1). To make the function more clear, we should be explicit with the return values similar to the other sign kernels.

Reporter: Eduardo Ponce / @edponce
Assignee: Eduardo Ponce / @edponce

Related issues:

• [C++][Compute] Add sign function kernels (is part of)

PRs and other links:

• GitHub Pull Request #11113

_{Note: This issue was originally created as ARROW-13937. Please see the migration documentation for further details.}

[asfimport]

David Li / @lidavidm:
Issue resolved by pull request 11113
#11113