Add code toolbar to Jupyter AI chat

[dlqqq]

Description

Adds a code toolbar to Jupyter AI chat that allows users to easily take code generated by Jupyter AI and insert it into their currently active notebook. It supports 4 actions:

1. Insert above active cell
2. Insert below active cell
3. Replace active cell
4. Copy to clipboard

Demo

Screen.Recording.2024-05-20.at.8.44.33.AM.mov

Implementation details

• Adds a new ActiveCellContext React context that allows any React component to get access to a set of actions to perform on the user's currently active cell. These actions are provided by methods on a new ActiveCellManager singleton class.
• Adds a new TooltippedIconButton component that provides an opinionated default for an MUI icon button with a tooltip.

Future work

When inserting/replacing content into the notebook, the console sometimes emits the error:

Error: Calls to EditorView.update are not allowed while an update is in progress

However, there seems to be no impact on the behavior/stability of the JupyterLab application after this error is logged. We are using what appears to be the official API for setting the content of a cell in JupyterLab 4, meaning that this error is likely unavoidable for the time being. More specifically, this PR replaces the content of the active cell via the method:

activeCell.editor?.model.sharedModel.setSource(content);

[JasonWeill]

I see the toolbar even if the AI model gives me an error. Seems like it would be better to suppress the toolbar in this case.

[JasonWeill]

I was surprised that the "Replace current cell" button took effect immediately, with no confirmation dialog, but the Undo command reverses any change that this makes.

[JasonWeill]

Generally looking good — I especially like how the buttons are accessible via the keyboard! Just a few questions and comments.

[JasonWeill]

Opened #791 and #792 as enhancements to follow up on this; good work!