The McNay Art Museum will be celebrating something big on Sunday: the very first major renovation of the museum’s grounds in its 67-year history. The $6.25 million makeover, which took nearly two years to complete, transformed the grounds from an enclosed campus hidden behind wrought-iron fences and dense hedges into a park-like expanse designed to be more welcoming. The project has been in the works for a long time. In 2005, board chairman Tom Frost hosted a series of focus groups, asking people from all over San Antonio what they thought of the museum. It was eye-opening for Frost, who served on the board from 1971 until his death in…