XPF: Add docs for Ctrl+Click menus on macOS (#660)

This is a new feature that will be added in 1.6.

Author: grokys

xpf/platforms/macos.md

@@ -17,7 +17,7 @@ However there are problems with this mapping:
 2. `ModifierKeys.Windows` is actually [not set in `Keyboard.Modifiers` in WPF](https://github.com/dotnet/wpf/blob/6634719e22053aab8e5e0db37618170494aea334/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Input/KeyboardDevice.cs#L207-L219)
 3. Common controls such as text boxes are expected to have different keyboard shortcuts in macOS, such as "Move the insertion point to the beginning of the previous word" being Option+Left Arrow on macOS instead of Control+Left Arrow
 
-## Automatic macOS Key Mapping
+### Automatic macOS Key Mapping
 
 To fix many of these problems, one can call the `XpfKeyboard.MapMacOSKeys()` method on startup. This would usually be done in the same place as [the XPF WinAPI shim setup](../third-party-libraries); that is, in the constructor of your `App` class or `Program.Main`:
 
@@ -45,6 +45,27 @@ Calling this method on macOS:
   - Option+Left Arrow-> Ctrl+Left Arrow
   - Option+Left Arrow -> Ctrl+Left Arrow
 
-## Automatic macOS Keyboard Mapping
+### macOS Custom Keyboard Mapping
 
-For more flexible key mapping you can [add custom key mappings](../advanced/key-mapping).
+For more flexible key mapping you can [add custom key mappings](../advanced/key-mapping).
+
+## Context Menus <MinVersion version="1.6" /> 
+
+On macOS, context menus can be opened by Ctrl+Clicking as well as by right clicking. You can enable this feature by setting `XpfMouse.ShowContextMenuOnMacOSCtrlClick` on startup. This would usually be done in the same place as [the XPF WinAPI shim setup](../third-party-libraries); that is, in the constructor of your `App` class or `Program.Main`:
+
+```csharp
+using System.Windows;
+using Atlantis;
+
+namespace XpfKeyboardMappingExample;
+
+public partial class App : Application
+{
+    public App()
+    {
+        XpfMouse.ShowContextMenuOnMacOSCtrlClick = true;
+    }
+}
+```
+
+Once this feature is enabled, it can be disabled on a per-control basis by handling the [`ContextMenuOpening` event](https://learn.microsoft.com/en-us/dotnet/desktop/wpf/advanced/how-to-handle-the-contextmenuopening-event#suppressing-any-existing-context-menu-and-displaying-no-context-menu) and checking the value of [`Keyboard.Modifiers`](https://learn.microsoft.com/en-us/dotnet/api/system.windows.input.keyboard.modifiers) and/or [`Mouse.LeftButton`](https://learn.microsoft.com/en-us/dotnet/api/system.windows.input.mouse.leftbutton) to determine how the context menu is being opened.