All TermControl/TermApp/TermConnection event handlers should be TypedEventHandlers

[DHowett-MSFT]

WinRT design guidelines dictate that event handlers should have two arguments, T and EventArgs. For any class T that produces an event, this ensures that the event handler can identify which instance of T fired the currently-handled event.

The signature for an event handler delegate should consist of two parameters: sender (IInspectable), and args (some event argument type, for example RoutedEventArgs).

Given that we are exposing an internal API, we can specify a more specific T than IInspectable.

C++/WinRT supports this by way of winrt::TypedEventHandler<T, Args...>.

We should move all the TermConnection, TermApp and TermControl event handlers to use TypedEventHandlers.

bonus

We can get rid of DECLARE_EVENT and DEFINE_EVENT, and augment DECLARE_EVENT_WITH_TYPED_HANDLER (and DEFINE...TYPED) to use typename class_type as the sender type, so that we don't need to repeat ourselves:

terminal/src/cascadia/inc/cppwinrt_utils.h

Lines 42 to 47 in 880272c

	#define DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(name, eventHandler, sender, args) \
	public: \
	winrt::event_token name(Windows::Foundation::TypedEventHandler<sender, args> const& handler); \
	void name(winrt::event_token const& token) noexcept; \
	private: \
	winrt::event<Windows::Foundation::TypedEventHandler<sender, args>> eventHandler;

-#define DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(name, eventHandler, sender, args) \
+#define DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(name, eventHandler, args) \
     public: \
-    winrt::event_token name(Windows::Foundation::TypedEventHandler<sender, args> const& handler); \
+    winrt::event_token name(Windows::Foundation::TypedEventHandler<typename class_type, args> const& handler); \     void name(winrt::event_token const& token) noexcept; \
     private: \
-    winrt::event<Windows::Foundation::TypedEventHandler<sender, args>> eventHandler;
+    winrt::event<Windows::Foundation::TypedEventHandler<typename class_type, args>> eventHandler;

which, when used, becomes:

-DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(PasteFromClipboard, _clipboardPasteHandlers, TerminalControl::TermControl, TerminalControl::PasteFromClipboardEventArgs);
+DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(PasteFromClipboard, _clipboardPasteHandlers, TerminalControl::PasteFromClipboardEventArgs);