Method IdxToWord
IdxToWord(List<Rune>, int, int)
Given a line of characters, returns the word which ends at idx
or null. Also returns null if the idx is positioned in the middle of a word.
Use this method to determine whether autocomplete should be shown when the cursor is at
a given point in a line and to get the word from which suggestions should be generated.
Use the columnOffset to indicate if search the word at left (negative),
at right (positive) or at the current column (zero) which is the default.
protected virtual string IdxToWord(List<Rune> line, int idx, int columnOffset = 0)