[C++] Add ascii_lower kernel

[asfimport]

Reporter: Maarten Breddels / @maartenbreddels
Assignee: Maarten Breddels / @maartenbreddels

Related issues:

• [C++] String algorithm library for StringArray/BinaryArray (is a child of)

PRs and other links:

• GitHub Pull Request #7357

_{Note: This issue was originally created as ARROW-9100. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 7357
#7357