Only assume sections are collapsible if they are wrapped in a div

Now toggle doesn't add collapsible-heading and icon classes by default
It first checks to see if there the section is wrapped in a div
meaning it has been modified by MobileFormatter. If the section is
not wrapped in a div, collapsible sections are not enabled on that page

Plus small code refactor in enable method

Bug: 73063
Change-Id: I79df94a6ba3c4893af1fbac5d79215f57275e377
Merge "Only assume sections are collapsible if they are wrapped in a div"