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 範例重現 Visual Studio Code Extension 中的格式化失敗問題。追蹤 Lua language server 如何解析及格式化這些運算式，然後確認兩個範例都不再回報語法問題，並且能正確格式化。