chore: update dompurify to ^3.2.1

As [DOMPurify 3.2.0 added TypeScript types][1], this means that we can
remove our dependency on the `@types/dompurify` package.

[DOMPurify 3.2.0 also adds the `HTML_INTEGRATION_POINTS` option][2],
which adds back support for `<foreignObject>`,
[which broke in DOMPurify 3.1.7.][3]

[1]: https://github.com/cure53/DOMPurify/releases/tag/3.2.0
[2]: e4caa67971
[3]: de2c05cd54

.changeset/neat-rabbits-bake.md

@@ -0,0 +1,5 @@
+---
+'mermaid': patch
+---
+
+Bump dompurify to `^3.2.1`. This removes the need for `@types/dompurify`.