Harper should try to detect "the" as a typo for "they"

This is a very common typo, I think it's one I make myself. I just spotted it in a blog:

> When these installers ran on Windows 95, the replaced the Windows 95 versions

Since "the" is in the dictionary, the `SpellCheck` linter can't flag it. It will need a dedicated linter.

Start by locating the existing SpellCheck linter and the code or tests that define dedicated linter behavior. Check how spelling exceptions and typo suggestions are represented, then add coverage for cases where “the” should be detected as “they.” Done means the reported blog-style sentence is flagged without treating ordinary uses of “the” as errors.

Written by the indexing model from the issue text.