8.0 compatibility

[jasongrout]

This PR aims to have the codebase compatible with ipywidgets 7 and ipywidgets 8.

This also drops support for python 3.6, which has reached EOL.

[jasongrout]

c154430 should be deleted after ipywidgets 8 is released - it's only there to force npm to choose the prerelease versions so we can test ipywidgets 8.

[mwcraig]

@jasongrout - This works for me locally now. Adding the dependency on css-loader fixed the odd error I showed you on Friday.

I have not fixed this use of ManagerBase in the sidecar tests. When I tried to change it following the migration guide I got an error that Type 'ManagerBase' is not generic.

[martinRenou]

When I tried to change it following the migration guide I got an error that Type 'ManagerBase' is not generic

This can be fixed by removing the <HTMLElement> part: ManagerBase<HTMLElement> -> ManagerBase

[mwcraig]

This can be fixed by removing the part: ManagerBase -> ManagerBase

Thanks, done. One of these days I should really try to learn typescript...

[mwcraig]

No idea why the extension isn't being installed...there was a compilation issue caused by openssl3 dropping support for md4 hashes, see https://stackoverflow.com/questions/69719601/getting-error-digital-envelope-routines-reason-unsupported-code-err-oss

[eteq]

Poking about the status of this one. Any sense whether this is a deep problem vs "just need to convince the CI to reognize the right version"?

[jasongrout]

I manually checked also that I could build the python package and install it with ipywidgets 7 and ipywidgets 8 and it worked correctly for the readme example.

[jasongrout]

We just released 0.5.2, which enables ipywidgets 8 support.