Fix `CodeGenerationFormat` to correctly handle trailing trivia when formatting list elements#2864

ahoppen merged 2 commits intoswiftlang:mainswiftlang/swift-syntax:mainfrom

roopekv:code-gen-keep-whitespace-after-comma-if-it-precedes-other-triviaroopekv/swift-syntax:code-gen-keep-whitespace-after-comma-if-it-precedes-other-triviaCopy head branch name to clipboard