Markdig-based MarkdownTextBlock doesn't support clicking hyperlinks

[Arlodotexe]

Looking through the new Markdig-based Markdown control, I'm not seeing any obvious way to handle clicked links in the consuming application.

I see the library has an AutoLinkParser that takes an AutoLinkOptions.OpenInNewWindow, but AutoLink seems to be centered around detecting and making raw links clickable in the renderer. It's not clear where or how link clicks are handled from code-behind.

Looking at another UI project that uses Mardig, markdig.wpf, we find that their sample app is routing "hyperlink clicks" through FrameworkElement CommandBindings. Digging further, they've connected this binding through a Hyperlink object that is passed to a custom wpf-based LinkInlineRenderer.

We'll need to create a similar custom link renderer in the MarkdownTextBlock control offered in Labs before we can move forward with this ticket.

Originally posted by @Arlodotexe in #512

[michael-hawker]

Think these are the TODOs that are missing for this feature?

Labs-Windows/components/MarkdownTextBlock/src/TextElements/MyHyperlink.cs

Lines 46 to 69 in eba3625

	public void AddChild(IAddChild child)
	{
	#if !WINAPPSDK
	if (child.TextElement is Windows.UI.Xaml.Documents.Inline inlineChild)
	{
	try
	{
	_hyperlink.Inlines.Add(inlineChild);
	// TODO: Add support for click handler
	}
	catch { }
	}
	#else
	if (child.TextElement is Microsoft.UI.Xaml.Documents.Inline inlineChild)
	{
	try
	{
	_hyperlink.Inlines.Add(inlineChild);
	// TODO: Add support for click handler
	}
	catch { }
	}
	#endif
	}

@nerocui is that correct? What's the difference between the Hyperlink and HyperlinkButton here?

[nerocui]

Both HyperLink and HyperLinkButton should support clicking event if the URI is setup correctly. The TODO is there because I wanted to support the case where the developer want to handle the event with custom logic. Like opening in other apps, adding additional logic or in case the URI is not standard web URL.