User interface suggesting share-room-link is an invite link while in fact it isn't

### Description

Enter a invite-only room. Click "Invite to this room" in the user list.

![2020-10-26T18:38:17
](https://user-images.githubusercontent.com/18213227/97207598-805f0980-17ba-11eb-9870-2ff6a4915854.png)

You will see the invite dialog:

![2020-10-26T18:36:08
](https://user-images.githubusercontent.com/18213227/97207677-9240ac80-17ba-11eb-9c84-1af1736557d8.png)

Click share this room. A matrix.to link is opened. Considering that this link was generated from the "Invite to this room" dialog one would assume that that link is an invite link. However, it is not, and if someone not already in the room tries to join the room using that link they will get an error message.

This is bad UX. It should be clear that the generated link is useless by itself and isn't sufficient to let someone enter the room.

Related to vector-im/element-meta#573, but this is not about making implementing invite links, but about the UX so that users don't think the link is an invite link while it in fact isn't.

### Version information

- **Platform**: Desktop, but concerns all.
- **OS**: Arch
- **Version**: 1.7.10