Custom link text can be used for phishing

### Your use case

This is a continuation of https://github.com/vector-im/element-web/issues/6532

Since Element allows users to use markdown links, it's possible to make a link look like it leads to a different website than it actually does, for example:

```markdown
[good.com](evil.com)
```

### Have you considered any alternatives?

Some discussion has happened in https://github.com/vector-im/element-web/issues/6532 with some proposed solutions. The solution that seems to gather most consensus seems to be adding an alert like the one Thunderbird has:


Which it looks like Element iOS already implements according to https://github.com/vector-im/element-web/issues/6532#issuecomment-674825464

### Additional context

I wasn't sure what template to use to file this issue. The original issue was triaged as an enhancement request so I went for that, but feel free to fix the labels if it's wrong. Ideally https://github.com/vector-im/element-web/issues/6532 could just be reopened (it was closed by mistake by a PR that didn't actually fix it) but I'm told this would confuse processes in place.