fix #101991 Ignore score command shortcuts in menus

Previously, certain keyboard shortcuts were active in menus when they
shouldn't be. For example, pressing the letter keys A to G while inside
a menu would cause notes to be added to the score, and S would add a slur.
This was problematic because letter keys are traditionally used to open
menu items (e.g. pressing A in the Help menu should open the About dialog).

This commit prevents unwanted edits from the menus by terminating the edit
operation if the score does not have focus. The shortcut is still active,
however, so this commit DOES NOT restore the traditional behaviour where
pressing letter keys opens menu items. As such, this is a quick fix rather
than a long-term solution. An investigation showed that a better solution
is not possible without significant changes to the shortcut system.

See description in PR #5890 for commentary on various potential ways to solve
this issue that were investigated and rejected in favor of this quick fix.

mscore/musescore.cpp

@@ -5879,6 +5879,10 @@ void MuseScore::cmd(QAction* a)
                tr("Command %1 not valid in current state").arg(cmdn));
             return;
             }
+      if (sc->assignedWidget() == MsWidget::SCORE_TAB && !ctab->isAncestorOf(QApplication::focusWidget())) {
+            qDebug("MuseScore::cmd(): not on score tab <%s>", qPrintable(cmdn));
+            return;
+            }
       if (cmdn == "toggle-palette") {
             showPalette(a->isChecked());
             if (a->isChecked()) {