Sunset magazine will make Cornerstone Sonoma the home of its main gardens and outdoor test kitchen, a move that is expected to revitalize the Sonoma Valley attraction by drawing a new wave of international attention — and visitors — to the region. The popular Time Inc. publication, known mostly for its lifestyle magazine and online website focusing on the West, announced Tuesday it is leaving its longtime campus in Menlo Park. It will move its editorial headquarters to Jack London Square in Oakland and relocate its gardens, where editors and staff test their ideas, to Sonoma.