Replace "hold to confirm" with "middle button"

[ibz]

We might eventually want to replace all instances of "hold to confirm" with the "middle button".

For now the most important place to do it is in confirm_more, which is used to confirm long messages.

It should look like this:

I am creating this issue so that I can work on #4601 without thinking about this change because it seems to affect many other places and it makes testing & reviewing that PR unnecessarily complicated, but eventually we can reuse this issue for other PRs dealing with TS3 "hold to confirm" throughout the code base.

[Hannsek]

Note: If we proceed with this change, we'll need to adjust the tutorial flow. "Hold to confirm" currently appears alongside the middle confirmation, and we shouldn't have the middle confirmation in the tutorial twice.