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/iter.lua

@@ -1313,8 +1313,11 @@ function IterArray.new(t)
   }, IterArray)
 end
 
-return setmetatable(M, {
+setmetatable(M, {
   __call = function(_, ...)
     return Iter.new(...)
   end,
 })
+
+-- Return M separately to work around EmmyLuaLs/emmylua-analyzer-rust#1240.
+return M