Is there a martial art that has Tekken 2's Lee's "back flip kick"?
To flesh out Sardathrion's answer, there isn't a martial art where you will find it as a serious maneuver used in a fight. Jumping kicks in general are risky business, since you are surrendering a great deal of control by leaving the ground, and actually hitting your opponent will bleed off a great deal of momentum, which is hazardous when you're inverting your body with the head to the ground. This is assuming that you either hit, or miss. It's also quite possible that your opponent will catch or otherwise deflect your kick in a way that you don't expect, which may further negatively impact your trajectory. And honestly, you're not going to get that much impact, particularly if you want to still have enough momentum to land on your feet.
That said, there are two martial arts that use such flip kicks in a more ritualized manner as a display of athletic skill that could theoretically be used offensively. As Sardathrion notes, a back-flip with a kick does exist in Capoeira, the back flip being refered to as a salto mortal and adding a kick sometimes being referred to as a "salto mortal com chapa*, literally "back flip with strike". You will also occasionally see this move in professional wrestling. In both cases, it is expected that there will be no contact, although in wrestling, the target is expected to act as if they were hit most of the time.
And, as noted in the comments, this is a common move in tricking, either with legs together in a layout, or with split legs as a "flash kick", although almost never being performed in a martial manner.
Lastly, while it doesn't actually apply directly to your question, since you're asking about Marshall Law, Bruce Lee didn't do the flip kick in Enter the Dragon. It was his stunt double, Yuen Wah.
So… he wanted me to double him for a back-flip. But, he actually knows how though… What does he know? Cartwheel. I would double him for the back-flip. So… when flipping over the monks, over their sleeves… I doubled him there. After passing them… flipping and landing, even his backside is me doubling Bruce walking like this. Doubled his backside walking too.
I think you are looking at capoeira.