LibVT: Enable caller to control the visibility of the scrollbar widget

In preparation for another feature, expose an API so that any users of
this widget can control the scrollbar visibility.

Userland/Libraries/LibVT/TerminalWidget.cpp

@@ -548,6 +548,11 @@ void TerminalWidget::set_opacity(u8 new_opacity)
     update();
 }
 
+void TerminalWidget::set_show_scrollbar(bool show_scrollbar)
+{
+    m_scrollbar->set_visible(show_scrollbar);
+}
+
 bool TerminalWidget::has_selection() const
 {
     return m_selection.is_valid();

Userland/Libraries/LibVT/TerminalWidget.h

@@ -43,6 +43,8 @@ public:
     void set_opacity(u8);
     float opacity() { return m_opacity; };
 
+    void set_show_scrollbar(bool);
+
     enum class BellMode {
         Visible,
         AudibleBeep,