Add an API for extracting information from .tl files?

[pdesaulniers]

In theory, this would be super useful for text editors, languages servers (teal-language/vscode-teal#16, teal-language/vscode-teal#17), tools such as #80...

Off the top of my head, I would like to be able to query things like

• What is the type of the variable at (y, x)?
• Where is the variable at (y, x) defined / implemented? Where is it referenced?
• Which variables are accessible in the lexical scope at (y, x)? What are their types?

With that said, tl's parser is not designed to deal with incomplete inputs right now, so I don't know how well this API would work in text editors in practice. For instance, some incomplete inputs can cause a cascade of errors:

local x = {
   y: 
}

-- the type checker is pretty much non-functional beyond this point

Perhaps this could be implemented as an external tool instead.

[pdesaulniers]

Implemented in #369 😁