Spec uses the term "recovery key" in a way that nobody else does

[richvdh]

Link to problem area: https://spec.matrix.org/v1.7/client-server-api/#recovery-key

Issue

The spec uses "recovery key" to refer to the private part of a key backup key.

Our clients (in both code and UI) use "recovery key" to mean a 4S key, which is a completely different sort of key (although they do use the same base58 algorithm for presentation to the user: 4S, key backup).

I propose that the spec avoid the term "recovery key" altogether, since it is so overloaded, and instead just say "key-backup decryption key" or something suitably long-winded but explicit.