Terminal/LibGUI::TextEditor: Add shift+return to search forwards

This adds support for shift+return key combo in single line TextEditor
fields. Used in this case for searching backwards/forwards in the
Terminal find window.

Userland/Applications/Terminal/main.cpp

@@ -190,6 +190,10 @@ static RefPtr<GUI::Window> create_find_window(VT::TerminalWidget& terminal)
         find_backwards.click();
     };
 
+    find_textbox.on_shift_return_pressed = [&]() {
+        find_forwards.click();
+    };
+
     auto& match_case = search.add<GUI::CheckBox>("Case sensitive");
     auto& wrap_around = search.add<GUI::CheckBox>("Wrap around");
 

Userland/Libraries/LibGUI/TextEditor.cpp

@@ -731,6 +731,12 @@ void TextEditor::keydown_event(KeyEvent& event)
         if (event.key() == KeyCode::Key_Tab)
             return AbstractScrollableWidget::keydown_event(event);
 
+        if (event.modifiers() == KeyModifier::Mod_Shift && event.key() == KeyCode::Key_Return) {
+            if (on_shift_return_pressed)
+                on_shift_return_pressed();
+            return;
+        }
+
         if (event.key() == KeyCode::Key_Return) {
             if (on_return_pressed)
                 on_return_pressed();

Userland/Libraries/LibGUI/TextEditor.h

@@ -138,6 +138,7 @@ public:
     Function<void(bool modified)> on_modified_change;
     Function<void()> on_mousedown;
     Function<void()> on_return_pressed;
+    Function<void()> on_shift_return_pressed;
     Function<void()> on_escape_pressed;
     Function<void()> on_up_pressed;
     Function<void()> on_down_pressed;