Allow empty string identifiers on non-flags enums in JsonStringEnumConverter and disallow non-flags comma-splitting#128285

Copilot wants to merge 4 commits into

maindotnet/runtime:mainfrom

copilot/fix-jsonstringenummembernameattributedotnet/runtime:copilot/fix-jsonstringenummembernameattributeCopy head branch name to clipboard