Prompt Rendering Performance improvements

Pull Request :ghpull:`11933` introduced an optimisation in the prompt rendering logic that should decrease the resource usage of IPython when using the _default_ configuration but could potentially introduce a regression of functionalities if you are using a custom prompt.

We know assume if you haven't changed the default keybindings that the prompt will not change during the duration of your input – which is for example not true when using vi insert mode that switches between [ins] and [nor] for the current mode.

If you are experiencing any issue let us know.