[QtConcurrent] Qt6 Example revamp

As a little reminder, QtConcurrent provides basically:

• map, mapped, mappedReduced
• filter, filtered, filteredReduced
• run, task
• usage of QFuture, QFutureWatcher etc.

I would suggest following modifications to the examples:

• imagescaling
  • Keep it as a widgets example showing all possibilities.
  • Update documentation to align with the example-guidelines

• progressdialog
  • The dialog progresses way to fast. I would suggest to modernize it.
  • Update documentation to align with the example-guidelines
• wordcount
  • Terminal application that shows the usage of map(). I would keep it
  • Maybe add a little widgets-dialog to select a path
  • Update documentation to align with the example-guidelines
• runfunction
  • Terminal application that provides not so much useful content. Either modernize it a little bit or merge it with the wordcount or progressdialog example.
• map
  • Terminal application that only shows the usage of blockingMapped(~).  As the wordcount example already shows this API usage and progressdialog shows the usage of filtered, which is very similar, I would remove it.

In general, I would say the API and logic of map and filter is overlapping and therefore easy to understand. With these changes we would still show full API usage.