build: enable more EmmyLua checks

- call-non-callable
- missing-fields
- redefined-label
- redefined-local
- undefined-field
- unreachable-code

Promote redefined-local and unreachable-code to warnings.

Fix DOS line-ending handling for multiline semantic tokens, and support
intersection types in the help parser.

AI-assisted

runtime/lua/vim/net.lua

@@ -107,6 +107,7 @@ function M.request(method, url, opts, on_response)
     return (b == nil and true) or (type(b) == 'string' and not b:match('^@'))
   end, true, 'body should be string and not start with @')
   vim.validate('on_response', on_response, 'function', true)
+  ---@cast on_response vim.net.request.ResponseFunc?
 
   local retry = opts.retry or 3