Support specifying globals inside Lua files

Currently, when using this language server, you get warnings for global variables:

if someGlobalVariable then -- Undefined global `someGlobalVariable `. Lua Diagnostics.(undefined-global)
  print("wow!")
end

The way to squelch them is to add the globals to the VSCode settings. But this is too much of a sledgehammer, as we might only want the globals to be enabled in this specific file. Thus, we should also add a feature so that end-users can specify the globals in-line:

-- We specify a list of globals at the top of the file.
-- @global someGlobalVariable 

someCode()

if someGlobalVariable then -- No warning.
  print("wow!")
end

先定位 language server 中未定義全域變數診斷的處理方式，以及現有的 VSCode 全域變數設定。追蹤 Lua 註解的解析方式，接著定義並測試內嵌 @global 語法，讓指定的全域變數只在該檔案中被接受，而不變更整個專案的設定。