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
Before this commit, we carried custom code and styles for the sidebar on
mobile. This meant the look and feel of bringing up the sidebar on
mobile was very different from the user menu resulting in a very
inconsistent experience on mobile. Also, we could not leverage on the
existing swipe to close support on mobile.
In this commit, we made it such that the sidebar dropdown is always
rendered on mobile and made the interaction with the dropdown more
consistent with the user menu. There is also more parity with the old
hamburger dropdown when the experimental sidebar is disabled.
