“You have likely never heard of Tommy Johnson, but it turns out that Johnson was, and still is, according to everyone who would know, ‘the most heard tubist on the planet.’ A first-chair studio musician in Hollywood for 50 years, Johnson played on thousands of recordings”; his was the breath behind those ominous shark-attack notes in “Jaws.” After Johnson’s death in October, a memorial concert was in order, and so on Sunday in Los Angeles, 99 tubists took the stage. “They came to honor their fallen tuba king.”