Automatic Vi prompt stripping

When pasting code into IPython, it will strip the leading prompt characters if there are any. For example, you can paste the following code into the console - it will still work, even though each line is prefixed with prompts (In, Out):

In [1]: 2 * 2 == 4
Out[1]: True

In [2]: print("This still works as pasted")

Previously, this was not the case for the Vi-mode prompts:

In [1]: [ins] In [13]: 2 * 2 == 4
   ...: Out[13]: True
   ...:
  File "<ipython-input-1-727bb88eaf33>", line 1
    [ins] In [13]: 2 * 2 == 4
          ^
SyntaxError: invalid syntax

This is now fixed, and Vi prompt prefixes - [ins] and [nav] - are skipped just as the normal In would be.

IPython shell can be started in the Vi mode using ipython --TerminalInteractiveShell.editing_mode=vi