Add the Ability to Specify a Separator in CommandBar#2253

cbowdoin wants to merge 4 commits intomicrosoft:mainmicrosoft/fluentui-apple:mainfrom

cbowdoin:user/cbowdoin/AddSeperatorSupportToCommandBarcbowdoin/fluentui-apple:user/cbowdoin/AddSeperatorSupportToCommandBarCopy head branch name to clipboard