Switching from code to markdown to code loses text

[rchiodo]

1. Create a new cell
2. Enter some code
3. Switch to markdown
4. Change code
5. Hit escape
6. Change back to code

Expected result:
Markdown is code

Actual result:
Code backs to before it was markdown

[rchiodo]

This is a state issue. During code cell change the state of the cell is not updated.

[rchiodo]

This would be much easier to fix if we did this first:
https://github.com/microsoft/vscode-python/issues/7949

[IanMatthewHuff]

Validated with the listed repro.