New test cases for inserting menus and menu items with position and/or referenced items.
Fix unit tests failures on Mac by adjusting expected menu positions.
Update two test cases that use non-existent reference id to expect "error-not-found".
Fix intermittent test failure.
Merge pull request #2588 from adobe/rlim/menu-position-api

New test cases for inserting menus and menu items with position and/or referenced items.