EW refers to "security key" instead of "recovery key"

[richvdh]

Users can create a passphrase which is used to encrypt their server-side secret storage; alternatively we can generate a key for them.

In the past we called the passphrase a "recovery phrase", or the generated key the "recovery key"; matrix-org/matrix-react-sdk#5533 changed the terminology to be "security phrase/key".

However, the Element product team have decided to switch back to "recovery key/phrase", per element-hq/element-meta#2394 (comment).

There are lots of references to "security key" throughout the application which will need an update. We'll also need to add some help text which says "recovery key was previously known as security key", or words to that effect.