Fixed yank cursor bug

- When yanking, there was a bug that made the cursor move to the very end of the yank selection, rather than moving the cursor to the beginning of the selection like vim does. After the yank, cursor now moves to start of selection.

- Also, @editor.getSelection() is deprecated, so we are now using editor.getLastSelection().
Rather than just measure the screen position, we get the range of the selection and use that to check the selection position.