Update editor example

[bugadani]

The goal of this PR is to improve the editor example to support vertical cursor movement.

• Words longer than a line are handled incorrectly. Might be an issue on line boundaries?
• There may or may not still be a small disagreement between the offsets with multiple empty lines.
• Click to move cursor
• Move displayed area if cursor moves out of view - coordinate based.
  Needs to track if cursor is at the end of line. Alternative is a one-frame delay.
• Move displayed area if cursor moves out of view - character offset based.
  Needs to specify that cursor coordinates are in "text space". Also, need to define "text space" vs "world space".
• Allow accessing plugins after drawing, remove Rc from plugin