Fix issues identified in 5.0.0b0, prepare 5.0.0b1

[krassowski]

References

Closes #969
Closes #974
Closes #973

Code changes

• implements isApplicable for kernel completion provider override
• switches to editor wrapper in diagnostics listing to enable scrolling to out-of-view cells
• improves support for windowed notebook but it is still imperfect (diagnostics may be not rendered if scrolling fast and then coming back)

User-facing changes

Changes the colour of highlights to slightly darker and removes dotted outline. Feedback welcome.

Backwards-incompatible changes

IEditorDiagnostic now uses editorAccessor instead of editor.

[github-actions]

👈 Launch a binder notebook on branch krassowski/jupyterlab-lsp/bugfixes

[bollwyvl]

I haven't yet gotten a working checkout up yet to even do a resolve, but perhaps this could this add || ^4.1.0.alpha0 to start looking at what's in main upstream? Seems likely 4.1.0 might be a more suitable target, anyway, if upstream changes will be needed.

[krassowski]

Ha, I've just commented on #917 (comment). This is not because of semver (it is fine).

[krassowski]

See 856e9f3.