Add separate commands for type-of/at

[meraymond2]

Change

https://github.com/meraymond2/idris-vscode/issues/71

Allows :type-of and :type-at to be called as commands, so they can be assigned to keyboard shortcuts. At the moment, they're only available on hover.

Output

I've gone with the output-channel to display the types. There are multiple ways of displaying information in VS, and none of them are great options.

• output channels lack syntax highlighting
• information messages don't allow newlines
• status bar would be too small and wouldn't allow newlines, modals would need closing
• for printing documentation and metavariables, I have been using virtual text documents, because the Idris 1 IDE provided syntactic highlighting for those. I think that would be too heavy for this. I'm tempted to switch all the Idris 2 docs to the output channel too, since there isn't any semantic highlighting yet, and it is more convenient than the virtual docs.