Union type with string literals not recognized with double quotes

[mfussenegger]

Thanks for the work on vimcats.

It looks like there's a small issue with union types using string literals that
use double quotes.

For example with:

local M = {}

---Hello
---
---@param x "foo"|"bar"
function M.name(x)
  print(x)
end

return M

With vimcats 1.1.0 the generated docs look like:

M.name()                                                                *M.name*


vim:tw=78:ts=8:noet:ft=help:norl:

Changing the literals to use single quote: ---@param x 'foo'|'bar' makes it work:

M.name({x})                                                             *M.name*
    Hello


    Parameters: ~
        {x}  ("foo"|"bar")


vim:tw=78:ts=8:noet:ft=help:norl:

Given that the union type examples in https://luals.github.io/wiki/annotations/
use double quotes I think it would be great if both variants worked.