Getting through security is a breeze. The terminal and concourses are still eerily quiet for long stretches of the day. And strange times have brought new amenities, including vending machines and kiosks that sell face masks. But for all the signs of the coronavirus pandemic’s continuing disruption of air travel, crowds are quickly growing inside Denver International Airport — and aboard planes — as more people venture farther from home this summer. “It’s actually surprising how full the planes are,” said Brieanna Martinez, as she waited with her two young children on Concourse B this week for a connecting United flight back home to Washington state.