LibGUI+Apps: Adjust Splitter spacings

Different thread highlights between widgets lead to different
visual weights between splitters, even when they have the same
width or height. This means some splitters look best at odd
sizes while others even. This sets the default spacing to the
most commonly used, depending on orientation, and adjusts
spacing for a few apps based on the new paint rect.

The most consistent look across apps requires some manual
tweaking occassionally. Knurlheads, use your discretion!

Userland/Applications/Help/main.cpp

@@ -100,7 +100,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto toolbar = TRY(toolbar_container->try_add<GUI::Toolbar>());
 
     auto splitter = TRY(widget->try_add<GUI::HorizontalSplitter>());
-    splitter->layout()->set_spacing(5);
+    splitter->layout()->set_spacing(4);
 
     auto manual_model = ManualModel::create();
 

Userland/Demos/WidgetGallery/GalleryGML/BasicsTab.gml

@@ -11,7 +11,9 @@
         }
 
         @GUI::HorizontalSplitter {
-            layout: @GUI::HorizontalBoxLayout {}
+            layout: @GUI::HorizontalBoxLayout {
+                spacing: 4
+            }
 
             @GUI::Frame {
                 name: "label_frame"

Userland/DevTools/HackStudio/HackStudioWidget.cpp

@@ -91,10 +91,10 @@ HackStudioWidget::HackStudioWidget(String path_to_project)
     auto& toolbar_container = add<GUI::ToolbarContainer>();
 
     auto& outer_splitter = add<GUI::HorizontalSplitter>();
-    outer_splitter.layout()->set_spacing(5);
+    outer_splitter.layout()->set_spacing(4);
 
     auto& left_hand_splitter = outer_splitter.add<GUI::VerticalSplitter>();
-    left_hand_splitter.layout()->set_spacing(5);
+    left_hand_splitter.layout()->set_spacing(6);
     left_hand_splitter.set_fixed_width(150);
     create_project_tab(left_hand_splitter);
     m_project_tree_view_context_menu = create_project_tree_view_context_menu();
@@ -110,7 +110,6 @@ HackStudioWidget::HackStudioWidget(String path_to_project)
     m_diff_viewer = m_right_hand_stack->add<DiffViewer>();
 
     m_editors_splitter = m_right_hand_stack->add<GUI::VerticalSplitter>();
-    m_editors_splitter->layout()->set_spacing(5);
     m_editors_splitter->layout()->set_margins({ 3, 0, 0 });
     add_new_editor(*m_editors_splitter);
 

Userland/Libraries/LibGUI/Splitter.cpp

@@ -27,7 +27,10 @@ Splitter::Splitter(Orientation orientation)
     set_background_role(ColorRole::Button);
     set_layout<BoxLayout>(orientation);
     set_fill_with_background_color(true);
-    layout()->set_spacing(3);
+    if (m_orientation == Gfx::Orientation::Horizontal)
+        layout()->set_spacing(3);
+    else
+        layout()->set_spacing(4);
 }
 
 Splitter::~Splitter()