Pulled from microsoft/vscode-python#11781

• insert cell above current cell
• insert cell below current cell
• insert cell at current line (start of cursor line and insert # %%\n)
• delete current cell
• toggle cell type code and markdown (ideally toggle to markdown would do a block line comment)
• cut current cell
• copy current cell
• select all current cell
• collapse current cell (for the code folding)
• split cell (auto insert # %% or equivalent -- Would a snippet suffice?)

cc @Yura52, @earthastronaut