danger: Check PR titles (#13053)

This PR sets up Danger to check PR titles for consistency, using
[`danger-plugin-pr-hygiene`](https://github.com/maxdeviant/danger-plugin-pr-hygiene).

<img width="919" alt="Screenshot 2024-06-14 at 11 16 31 AM"
src="https://github.com/zed-industries/zed/assets/1486634/167fe698-2505-422b-8e41-e121d9fe933f">

Release Notes:

- N/A

script/danger/dangerfile.ts

@@ -1,4 +1,12 @@
 import { danger, warn } from "danger";
+const { prHygiene } = require("danger-plugin-pr-hygiene");
+
+prHygiene({
+  rules: {
+    // Don't enable this rule just yet, as it can have false positives.
+    useImperativeMood: "off",
+  },
+});
 
 const RELEASE_NOTES_PATTERN = new RegExp("Release Notes:\\r?\\n\\s+-", "gm");