feat: Add C# snippet for quick define AvaloniaProperty and RoutedEvent.

[workgroupengineering]

Add following snippet to C#

Shortcut	Description
aap	AttachedProperty
adp	DirectProperty
asp	StyledProperty
are	RoutedEvent

[prashantvc]

This is great, do you want to bring them to VS Code extension too too?
https://github.com/AvaloniaUI/AvaloniaVSCode

Snippet guide:
https://code.visualstudio.com/api/language-extensions/snippet-guide

[workgroupengineering]

I have little experience with VS Code, but I'll give it a try

[maxkatz6]

Rider has most of these snippets with other names:
https://github.com/ForNeVeR/AvaloniaRider/blob/0e7782c498658e8a787b7a0b35fe247a86b5266d/src/extensions/settings/liveTemplates.DotSettings

While I don't have an opinion on which name is better, I think consistency is important here, to avoid confusion between IDEs.

[workgroupengineering]

I aligned the snippet shortcuts to Raider, but they don't seem like shortcuts to me 😄.