Spec: Integrate the specification for match types. (#22164)

Relevant section of the type definitions page:

![image](https://github.com/user-attachments/assets/becabfbe-6ae5-4a16-8554-7cffa5aeb7e8)
and the full rendering of the Types page:

![image](https://github.com/user-attachments/assets/b9311b20-63b4-44ce-92b2-bf101e2b86fb)

Author: odersky