Author Lumino 1 → Lumino 2 migration guide

[afshin]

While we produce change logs automatically, we'll need something more substantial with examples and some narrative to help users migrate their code with the Lumino update. This document will complement the JupyterLab 3 → JupyterLab 4 migration guide for extension authors.

[3coins]

@afshin This looks like a good exercise for me to learn more about Lumino. Is handling this by package the correct approach?

[afshin]

I think handling this by looking at open and closed issues in the Lumino 2 milestone might be good because you'll see everything that's being modified or removed, there.

[afshin]

The top-level comment for this PR lists out all the API changes that PR contains and is relevant here:

• Use native iterators instead of Lumino iterators #346

[afshin]

There is now a migration.md file in the docs that includes the documentation for iterators.