Problems with the it's→its linter

**Describe the bug**

1. `it's` with an ASCII apostrophe is linted to change to `its` but `it’s` with a Unicode apostrophe is not.
2. The `LintKind` is erroneously set to `Agreement` but that's for things like "these is" or "they says" where two POSes that have properties that must "agree", such as "number" (singular vs plural). This is a kind of spelling mistake but `Punctuation` is a tighter fit.

**Screenshots**

`it's` with an ASCII/typewriter apostrophe is linted:

`it’s` with a typesetting/"smart" apostrophe is not linted:

Locate the linter rule handling “it's” and the code assigning its LintKind. First compare the ASCII and Unicode apostrophe cases, then add or update focused tests so both forms are linted consistently and the classification is Punctuation rather than Agreement.

Written by the indexing model from the issue text.