Add split right & split down menu entries for the GTK apprt.

Inspired by #1752

src/apprt/gtk/App.zig

@@ -340,6 +340,8 @@ fn syncActionAccelerators(self: *App) !void {
     try self.syncActionAccelerator("win.close", .{ .close_surface = {} });
     try self.syncActionAccelerator("win.new_window", .{ .new_window = {} });
     try self.syncActionAccelerator("win.new_tab", .{ .new_tab = {} });
+    try self.syncActionAccelerator("win.split_right", .{ .new_split = .right });
+    try self.syncActionAccelerator("win.split_down", .{ .new_split = .down });
 }
 
 fn syncActionAccelerator(
@@ -678,6 +680,8 @@ fn initMenu(self: *App) void {
         c.g_menu_append_section(menu, null, @ptrCast(@alignCast(section)));
         c.g_menu_append(section, "New Window", "win.new_window");
         c.g_menu_append(section, "New Tab", "win.new_tab");
+        c.g_menu_append(section, "Split Right", "win.split_right");
+        c.g_menu_append(section, "Split Down", "win.split_down");
         c.g_menu_append(section, "Close Window", "win.close");
     }
 

src/apprt/gtk/Window.zig

@@ -162,6 +162,8 @@ fn initActions(self: *Window) void {
         .{ "close", &gtkActionClose },
         .{ "new_window", &gtkActionNewWindow },
         .{ "new_tab", &gtkActionNewTab },
+        .{ "split_right", &gtkActionSplitRight },
+        .{ "split_down", &gtkActionSplitDown },
         .{ "toggle_inspector", &gtkActionToggleInspector },
     };
 
@@ -509,6 +511,32 @@ fn gtkActionNewTab(
     gtkTabNewClick(undefined, ud);
 }
 
+fn gtkActionSplitRight(
+    _: *c.GSimpleAction,
+    _: *c.GVariant,
+    ud: ?*anyopaque,
+) callconv(.C) void {
+    const self: *Window = @ptrCast(@alignCast(ud orelse return));
+    const surface = self.actionSurface() orelse return;
+    _ = surface.performBindingAction(.{ .new_split = .right }) catch |err| {
+        log.warn("error performing binding action error={}", .{err});
+        return;
+    };
+}
+
+fn gtkActionSplitDown(
+    _: *c.GSimpleAction,
+    _: *c.GVariant,
+    ud: ?*anyopaque,
+) callconv(.C) void {
+    const self: *Window = @ptrCast(@alignCast(ud orelse return));
+    const surface = self.actionSurface() orelse return;
+    _ = surface.performBindingAction(.{ .new_split = .down }) catch |err| {
+        log.warn("error performing binding action error={}", .{err});
+        return;
+    };
+}
+
 fn gtkActionToggleInspector(
     _: *c.GSimpleAction,
     _: *c.GVariant,