tools: enable array-callback-return ESLint rule

For array methods that depend on a callback (such as .filter() or .map()), require a return value from the callback.

First two commits fix a few issues in our code base that would be flagged by this rule.

Third commit enables the rule itself.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

tools readline test