The work was done by tcberner and myself, with thanks to antoine for the
exp-run.

Not a lot to report compared to other Qt5 updates:
* net/qt5-network is still broken with LibreSSL. I said this in a commit
  message ages ago but it bears repeating: upstream is open to adding support
  for LibreSSL, but someone needs to step up to maintain it upstream, otherwise
  things will continue to be broken all the time.
* www/qt5-webengine is a huge monster that is terrible to update, just like
  www/chromium itself is. We (kde@) have decided to keep using the 5.9 series
  for the time being, as it should be compatible with the rest of Qt anyway. It
  was updated to 5.9.5, the latest 5.9 release at the time of writing.

PR:		228213