addGlow

Given a range and a Glow, apply that glow to the characters in that range, which consists of zero-based indices of the start and end inclusive. Add a highlight for the first character, the middle region if any, and the last character of that range. A size-one range acts as both a first and last character, with no middle part. This simplifies rendering of a box highlight, since the highlight mechanism is executed for each styled run separately, with no easy way to tell if the left or right walls of the box should be drawn.

Answer the list of objects that Swing produced to represent the highlight areas.