Error message for "Room was previously configured to use encryption, but is no longer." is now swallowed rather than presented to the user

### Steps to reproduce

Go to an e2ee room whose m.room.encryption event has been reset and send a message. (In this instance, it hasn't deliberately been reset, but the client has got confused)

### What happened?

The relevant error ends up in the JS console however:

```
sendEvent of type m.room.message in !kGLhQmvYrFWnVNxhBx:matrix.org with txnId m1628524623349.189
16:57:03.366 rageshake.js?432e:65 setting pendingEvent status to encrypting in !kGLhQmvYrFWnVNxhBx:matrix.org event ID ~!kGLhQmvYrFWnVNxhBx:matrix.org:m1628524623349.189 -> undefined
16:57:03.383 rageshake.js?432e:65 Error sending event Error: Room was previously configured to use encryption, but is no longer. Perhaps the homeserver is hiding the configuration event.
at Crypto.encryptEvent (webpack-internal:///164:2598:13)
at MatrixClient.encryptEventIfNeeded (webpack-internal:///118:3151:24)
at eval (webpack-internal:///118:3057:38)
consoleObj. @ rageshake.js?432e:65
16:57:03.384 rageshake.js?432e:65 setting pendingEvent status to not_sent in !kGLhQmvYrFWnVNxhBx:matrix.org event ID ~!kGLhQmvYrFWnVNxhBx:matrix.org:m1628524623349.189 -> undefined
```

So this is a regression where we should be showing the human-facing error to the user, but we're not any more since we redesigned the error UI a few months ago.

### What did you expect?

Error should be presented to the user in the UI like we used to.

### Operating system

macOS

### Application version

nightly today

### How did you install the app?

_No response_

Start by tracing the send flow from MatrixClient.encryptEventIfNeeded to Crypto.encryptEvent, using the reported console error as the reproduction point. Then inspect the redesigned error UI and the pending-event transition to not_sent. Done means this encryption error is presented to the user in the UI rather than only logged to the console.

Written by the indexing model from the issue text.