LibLine: Add a hook to run when an interrupt is handled

We do not want to clog up signal handlers by putting possibly complex
logic inside them, so allow the editor to handle that.

Libraries/LibLine/Editor.cpp

@@ -171,6 +171,10 @@ String Editor::get_line(const String& prompt)
 
                 m_buffer.clear();
                 m_cursor = 0;
+
+                if (on_interrupt_handled)
+                    on_interrupt_handled();
+
                 m_refresh_needed = true;
                 continue;
             }

Libraries/LibLine/Editor.h

@@ -134,6 +134,7 @@ public:
 
     Function<Vector<CompletionSuggestion>(const String&)> on_tab_complete_first_token;
     Function<Vector<CompletionSuggestion>(const String&)> on_tab_complete_other_token;
+    Function<void()> on_interrupt_handled;
     Function<void(Editor&)> on_display_refresh;
 
     // FIXME: we will have to kindly ask our instantiators to set our signal handlers