BUG: 当_ENV作为多重赋值的第一个变量时, 后续变量会错误的识别成局部变量.

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这是非常罕见的场景, 并且建议避免编写这种代码.

```lua
local env = _ENV
_ENV, a = {}, 1
env.print(env.a, a) -- 1 nil
```
使用`parser.compile`函数解析得到的`state.ast.locals`会多出错误的局部变量`_ENV`和`a`.
整个多重赋值语句都会识别成`local`变量定义, 不管是`a, a.x, a[1]`形式, 生成的`ast.type`字段都会被错误的标识成`'local'`.

同时也会导致[vscode插件](https://github.com/LuaLS/lua-language-server)错误提示.

Start by reproducing the Lua snippet through parser.compile and inspect state.ast.locals and the ast.type values for each assignment target. Compare the result for _ENV, a, a.x, and a[1]; done means the assignment no longer creates incorrect local variables or marks every target as 'local'.

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