Welcome back to TechCrunch Mobility — your central hub for news and insights on the future of transportation. To get this in your inbox, sign up here for free — just click TechCrunch Mobility! Today is Juneteenth, a U.S. federal holiday marking the end of slavery in the United States.  About 10 years ago, there was a lot of chatter about who was winning the self-driving car race. One of the problems with that debate — besides assuming there would be just one winner — was that no one had a reliable way to measure it. This was an early...