ENG-54: Check spanners when assessing emptiness

Previously, a staff's emptiness was calculated based on its note and
annotation content. Since this is evaluated before the system was laid
out, the system did not have pointers to its SpannerSegments. This
commit adds a way to include whether a staff has any spanners
(particularly pedal markings and hanging slurs) in assessing emptiness,
creating more consistent/expected hiding behavior in HideMode::AUTO.

Duplicate of musescore#8430, part 2

libmscore/layout.cpp

@@ -1328,6 +1328,10 @@ void Score::hideEmptyStaves(System* system, bool isFirstSystem)
       int staffIdx = 0;
       bool systemIsEmpty = true;
 
+      Fraction stick = system->measures().front()->tick();
+      Fraction etick = system->measures().back()->endTick();
+      auto spanners = score()->spannerMap().findOverlapping(stick.ticks(), etick.ticks());
+
       for (Staff* staff : qAsConst(_staves)) {
             SysStaff* ss  = system->staff(staffIdx);
 
@@ -1339,6 +1343,12 @@ void Score::hideEmptyStaves(System* system, bool isFirstSystem)
                     && !(isFirstSystem && styleB(Sid::dontHideStavesInFirstSystem))
                     && hideMode != Staff::HideMode::NEVER)) {
                   bool hideStaff = true;
+                  for (auto spanner : spanners) {
+                        if (spanner.value->staff() == staff) {
+                              hideStaff = false;
+                              break;
+                              }
+                        }
                   for (MeasureBase* m : system->measures()) {
                         if (!m->isMeasure())
                               continue;