OutputPane: Use setter for priority and fix default visibility

Do not show the buttons of output views with priority < 0 (instead of
only == -1). Reduce the number of buttons that are shown by default to
the essential ones.

Change-Id: I5b44f18537b3033ce9d616f044a8b54b76988783
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/coreplugin/messageoutputwindow.cpp

@@ -22,6 +22,8 @@ MessageOutputWindow::MessageOutputWindow()
 {
     setId("GeneralMessages");
     setDisplayName(Tr::tr("General Messages"));
+    setPriorityInStatusBar(-100);
+
     m_widget = new OutputWindow(Context(Constants::C_GENERAL_OUTPUT_PANE), zoomSettingsKey);
     m_widget->setReadOnly(true);
 
@@ -72,11 +74,6 @@ void MessageOutputWindow::append(const QString &text)
     m_widget->appendMessage(text, Utils::GeneralMessageFormat);
 }
 
-int MessageOutputWindow::priorityInStatusBar() const
-{
-    return -1;
-}
-
 bool MessageOutputWindow::canNext() const
 {
     return false;