Fix memory leaks

[fcollonval]

References

Follow-up of jupyterlab/benchmarks#100 that introduces memory leaks analysis

Code changes

• Remove widget.id from various mapping
• Disconnect correctly signals following notebook switch in cell tags
• Dispose the sharedModel when switching it
• Dispose modelDB when a model is disposed
• Release disposable items in open with menu in context menu
• Clear settings connection in execution indicator

User-facing changes

None

Backwards-incompatible changes

N/A

[jupyterlab-probot]

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[fcollonval]

@meeseeksdev please backport to 3.4.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 3.4.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 6bf3f3b285f238b28e8e3b47e3f3a65249c41513

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #12750: Fix memory leaks'

4. Push to a named branch:

git push YOURFORK 3.4.x:auto-backport-of-pr-12750-on-3.4.x

5. Create a PR against branch 3.4.x, I would have named this PR:

"Backport PR #12750 on branch 3.4.x (Fix memory leaks)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.