In Tesla$$s $2018$ annual report, it stated: $$In March $2018,$ our stockholders approved a new $10-$year CEO performance award for Elon Musk with vesting contingent on achieving market capitalization and operational milestones $($the $2018$ CEO Performance Award$).$ Consequently, we may incur significant additional non$-$cash stock$-$based compensation expense over the term of the award as each operational milestone becomes probable of vesting.$$ What was the type of stock$-$based compensation approved in the $2018$ CEO Performance Award