Need to flag `that's` used as a possessive relative pronoun instead of `whose`

Some people feel that using "whose" with inanimate subjects is wrong, but it's not. `That's` is only a contraction of "that is" or "that has".

I just heard this on YouTube for the second time in less than a week. I didn't collect the first one but here's the second:

> And how could we forget "I am rich", which was a thousand dollar app **that's** pure function was to literally just flex.

Here's some other ways to avoid `that'` in such sentences:

- "...an app, the pure function of which was to literally just flex."
- "...a thousand-dollar app with the pure function of literally just flexing."
- "...a thousand-dollar app functioning purely to literally just flex."
- "...a purely functional thousand-dollar app built to literally just flex."

No file, test, or entry point is named in the issue. Start by locating the grammar-checking rule definitions for possessive relative pronouns, then add coverage for `that's` used where `whose` is intended and verify that contractions of “that is” or “that has” are not flagged.

Written by the indexing model from the issue text.