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/ftplugin/help.lua

@@ -96,7 +96,8 @@ local function runnables()
 
       if name == 'code' then
         local code = vim.treesitter.get_node_text(node, 0)
-        local lang_node = match[metadata[id].lang][1] --[[@as TSNode]]
+        local lang_id = metadata[id].lang --[[@as integer]]
+        local lang_node = match[lang_id][1]
         local lang = vim.treesitter.get_node_text(lang_node, 0)
         for i = start + 1, end_ do
           code_blocks[i] = { lang = lang, code = code }