`UIFeature.widgets` flag breaks Jitsi calls

#### Description

Hiding the widgets makes it impossible to have Audio- and Video Calls with more than two participants.

#### Steps to reproduce

- Set `UIFeature.widgets` to `false`
- join a room with >2 members
- when an audio- or video-call is started in that room you can't join it.

> Video conference started by hex-m
> Join the conference at the top of this room

But no Widget is shown at the top of the room.

If you start a Video Call yourself you won't be able to remove it again.

#### Possible solutions

As the Jitsi Meet widget is deeply integrated it should be treated differently and should not be hidden. Otherwise the UX is inconsistent.

Alternatively warn in the [documentation](https://github.com/vector-im/element-web/blob/develop/docs/config.md#ui-features) that `voip` and `widgets` should only be disabled together.

Alternatively replace Jitsi Meet with native Matrix group calls. (https://github.com/vector-im/element-web/issues/17424)