FB11662176 - Bring "Manage Extensions" widget to Safari Mac toolbar

[lapcat]

In Mobile Safari there's a "Manage Extensions" toolbar widget. This is very convenient, so please bring it to Mac Safari. If there's a Manage Extensions toolbar widget on Mac, then users won't need to put all Safari extension icons in their toolbar. This can be problematic if you have many Safari extensions installed. Firefox and Google Chrome both have toolbar widgets to manage extensions, so Safari Mac is the outlier.