Bug 41403

InsertListCommand's doApply mainly implements insertion and removal of lists in single paragraph. To handle a selection with multiple paragraphs, doApply calls modifyRange, which iterates over paragraphs in the selection and calls doApply on each paragraph. doApply calls modifyRange whenever the selection is a range object and returns except when the starting and the ending of the selection is in the same paragraph in which case modifyRange bails out by returning false and doApply proceed with its list insertion & removal. However, this peculiar structure makes the code harder to read and it has been an obstacle in debugging the bug 32422. I propose to merge InsertListCommand's modifyRange with doApply and isolate the logic for single paragraph case into a separate method.