Reduce signature flickering

[krassowski]

References

Fixes #834

Code changes

EditorTooltipManager gest new methods: showOrCreate, show, hide

User-facing changes

Signature tooltip will be hidden (rather than removed) if we know that we will be showing it again soon; if it has not changed (nor position, editor, etc), it will be shown as-is, if only content changed it will be updated.

Unfortunately, pylsp seems to return a message with empty signature every other time which is the direct cause of flickering in remaining instances.

Backwards-incompatible changes

Chores

• [x] linted
• [ ] tested
• [ ] documented
• [x] changelog entry

[github-actions[bot]]

:point_left: Launch a binder notebook on branch krassowski/jupyterlab-lsp/prevent-signature-flicker

[krassowski]

Flaky completion test unrelated, fixed in #861.