Add support for listing active snippets

[pokey]

For discoverability, it would be great to have a command to list all snippets that are active in the given context.

We should probably support a description field to our snippet format so that we can potentially show that in the list for snippets which have a description

[Mark-Phillipson]

I currently have this written in dotnet with a database behind it: https://www.screencast.com/t/LUCDd3Upcvx
https://voicelauncherblazor.azurewebsites.net/languages

[AndreasArvidsson]

Definitely doable. I just wonder what we actually want to show. The ones that have a phrase so you can just use the snippet command? Also include snippets without a phrase in case you used them for something custom? Also wrapper snippets? Do we want to have different groupings depending on with category they belong to? Or we could do some kind of suffix?

Neither solution is particular hard I just want us to iron out what we actually want before we start implementing.