This PR renames the old Sidebar::Section displaySection function
to displaySectionContent, and changes the meaning of displaySection
to hide the entire sidebar section including the header. This is
implemented via an arg passed to Sidebar::Section, which will default
to true if it is not passed, and the BaseCustomSidebarSection class
implements a default of `return true` for this function.
The following changes are made in this commit:
1. Move caret icon in sidebar section header to the right.
1. Each row in sidebar takes the full width which enables us to do a
full width highlight on hover and when sidebar link is active.
1. Ensure each row in Sidebar is of the same height.
Internal refs: /t/70546, /t/72196, /t/71820
