A proposed billionaire tax had Mark Zuckerberg thinking about leaving California. Provisions around the 2-for-1 split of Meta Platforms’ stock are designed to keep him in the state—and help him pay a potential tax bill. As Meta’s board negotiated the terms of the share split with the CEO, Zuckerberg told directors he was evaluating whether to leave the state in response to a proposed first-of-its-kind wealth tax, according to a new regulatory filing. Proposition 40, proposed by a healthcare union, would levy a one-time, 5% tax on the net worth of those with net assets of $1 billion or more…