VS Code extension: "insert code cell" behavior from inside a code cell

[juliasilge]

If you have a code cell like this, with your cursor on the empty line at 🌟:

```{python}
1 + 1
🌟
2 + 2

and you do "insert code cell", either via keyboard shortcut or the command palette, then you get this result:

1 + 1

2 + 2

We are finding that this is quite surprising to users and not what they want/expect. Instead they want output like what you get when taking the same action in RStudio:

1 + 1

2 + 2