Modernize Handlebars and improve security documentation in sandbox sample#1621

RinZ27 wants to merge 1 commit intoGoogleChrome:mainGoogleChrome/chrome-extensions-samples:mainfrom

RinZ27:fix/upgrade-handlebars-and-security-notesRinZ27/chrome-extensions-samples:fix/upgrade-handlebars-and-security-notesCopy head branch name to clipboard