[ic-side-navigation] allow icon only

Currently side-nav only allows a slotted icon along with a required app-title, could we de-couple these elements to allow an icon only variant of side-nav application name?

Consider use-case where the name of the application is included in the brand/icon.

Start by locating the ic-side-navigation component and its associated tests. Check how the slotted icon and required app-title are currently validated or rendered. Done means an icon-only side-nav application name is supported while the existing icon-and-title variant continues to work.

Written by the indexing model from the issue text.