fix #32866: score jumping issues

There are a bunch of related issues I am trying to fix together.  The fixes are related enough that I think it best to make and test them together, but  I will annotate the changes in the commentsto show which issue is actually fixed by which change.

The underlying problem here is that adjustCanvasPosition is called too often and/or with too broad a target.  This is in part because Score objects emit posChanged signals any time you click a note:

https://github.com/musescore/MuseScore/blob/396c44f97d090d7fcfbcc8f1e40506e7c5647c28/libmscore/score.cpp#L3431

This causes all scoreviews to respond, when really, only the current scoreview usually needs to.  Furthermore, there is not enough of the original context (eg, which note was clicked to trigger this) to be able to position the score well.  I guess there isn't a more focused call to adjustCanvasPosition in order to maintain the separation between libmscore and mscore.  Or may it is intended that in some cases, all scoreviews *should* respond.  In any case, I elected to leave this alone, and instead deal with the problems on the scoreview side.

There are also other places where adjustCanvasPosition is called unnecessarily, or with to broad a target.
I don't completely follow, but I tried this out, and I'm not sure I understand what is meant to be different about it.  It still fails in the case as my code - page with >1 system.  But your code looks cleaner - doesn't require separate cases - and in any event, as I mentioned before, the multiple-system-per-page really is not nearly as important as getting the single-system case right.  And both versions do this.

BTW, in case it isn't totally clear what the problem case is: create a score with four staves per system and make sure you can fit at least two systems on the page.  Zoom way in so only two or three staves fit on screen, position the canvas to view the last staff of the system, click a note on the last staff, and hit play.  When the playback hits the end of the system, the canvas does jump to the next system as it should, but it jumps to the *top* of the next system rather than keeping the display focused on the bottom staff.