typescript: Highlight `infer` keyword (#14696)

This PR adds syntax highlighting to TypeScript's
[`infer`](https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#inferring-within-conditional-types)
keyword.

Theme used: Sandcastle

**Before:**

![image](https://github.com/user-attachments/assets/e082cc8c-2e12-4cfa-a641-40324dd93f31)

**After:**

![image](https://github.com/user-attachments/assets/6263b5b2-19c8-4b64-87b6-ceead947bc03)



Release Notes:

- Added syntax highlighting to TypeScript's `infer` keyword
([#14696](https://github.com/zed-industries/zed/pull/14696))