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

首先定位 language server 中未定义全局变量诊断的处理逻辑，以及现有的 VSCode 全局变量设置。追踪 Lua 注释的解析方式，然后定义并测试内联 @global 语法，使指定的全局变量仅在该文件中被接受，而不改变项目范围的设置。