Expose actions, scopes, and snippets from extension to Talon

[pokey]

• This way talon side gets updated as infrequently as possible; just defining a grammar and all the vocabulary is up to the extension
• Include spoken forms in extension side
• Snippets include spoken form
• Snippets know whether they're active
• Actions include description that could be displayed in cheatsheet

Relies on cursorless-dev/command-server#8

We might want to do this one using something like a972e7a