By Hannah Lang WASHINGTON (Reuters) – The dollar slipped on Thursday with investors on edge at the end of the year as initial optimism over China’s reopening fizzled out and as markets processed a readout of U.S. jobless claims. Markets are weighing the impact of China’s rapid loosening of its strict COVID-19 rules with a surge in new infections. “China is one of the keys I think to 2023 and what happens to the global economy,” said Chris Gaffney, president of world markets at TIAA Bank. Following China’s removal of its quarantine rule for inbound travelers from Jan. 8, the United States, Japa…