57477: merge pastes list into target list
57989: Pasting list items into list can orphan last list item
66579: copy/paste of list item into another list items causes caret
mostly a refactoring and improvement of nsHTMLEditor::InsertHTMLWithCharsetAndContext()
git-svn-id: svn://10.0.0.236/trunk@97252 18797224-902f-48f8-a5cc-f745e15eee43