runners/spellchecker: Add autotests

1. `testDefaultDictionary`: Test the runner can return a suggestion.
   (spell hello)
2. `testSpecifiedDictionary`: Test the runner can return a suggestion
   when the language is specified. (spell en_US hello)
3. `testAutomaticDictionary`: Test the runner can return a suggestion
   when the term is not in the default language. (spell мама)
4. `testSuggestions`: Test the runner can return a suggestion when the
   term is misspelled.

CCBUG: 439544