Experimental cell execution analysis

[rebornix]

Re #14316.

This PR adds experiments for running code analysis upon cell execution, on top of which we can offer features like Gather Cells or Select/Run Dependent Cells. This requires the latest prerelease of Pylance extension for now.

The changes are contributed in standalone component and written in the same fashion as a standalone extension.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR).
• Title summarizes what is changing.
• Appropriate comments and documentation strings in the code.
• Has sufficient logging.
• Has telemetry for feature-requests.
• Unit tests & system/integration tests are added/updated.
• Test plan is updated as appropriate.
• package-lock.json has been regenerated by running npm install (if dependencies have changed).

[amunger]

seems unusual to have another file named extension.ts