This uses the field component in the bug report dialog, which generally improves
the styling to fit in more naturally with the rest of the app so that it feels
more trustworthy.
Fixes https://github.com/vector-im/riot-web/issues/9343
* Make it use BaseDialog / DialogButtons (also gives it has a top-right 'x' &
escape to cancel works)
* Stop misusing the 'danger' CSS class on the buttons. There is nothing dangerous
about submitting logs.
* Continued campaign against 'Click here' links.
Fixes https://github.com/vector-im/riot-web/issues/6622
