Doc: Clean up docs for PathView.highlightRangeMode enum values

Fix PathView.NoHighlightRange description, move the enum values
into a list, and do some minor editing.

Task-number: QTBUG-16160
Change-Id: I5356c21ea3244ce43defa346da11696a8706c71f
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>