Support optional chaining

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

Windows

What is the issue affecting?

Formatting

Expected Behaviour

        if weaps[i]?.serial ~= tempInv[i].vars.serial then
            if weaps[i]?.obj then
                DeleteObject(weaps[i].obj)
                weaps[i] = nil
            end
            GiveWeap(tempInv[i])
        end

Actual Behaviour

syntax Problem '?'

Reproduction steps

1. Go to '...'
2. Click '...'
3. See error '...'

Additional Notes

No response

Log File

No response

首先，使用 issue 中的 optional-chaining 示例重现 Visual Studio Code Extension 中的格式化失败问题。跟踪 Lua language server 如何解析和格式化这些表达式，然后验证两个示例都不再报告语法问题，并且能够正确格式化。