Remove content-visibility css prop to avoid jumpy scrollbar

[echarles]

References

Fixes #10428

Code changes

Remove content-visibility css prop to avoid jumpy scrollbar. This had been identified during the work on the 2.3 branch, but for some reason, the content-visibility prop has been pulled in master branch. This property does not bring any value to the performance as the virtual rendering is ensured by ad-hoc intersection observer.

User-facing changes

No more jumpy scrollbar as reported in #10428 (comment)

Backwards-incompatible changes

None

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[blink1073]

LGTM, thanks! I kicked the CodeQL build

[echarles]

Thx @blink1073

CodeQL is failing with the following unrelated?

  [2021-06-29 15:21:25] [build-stderr] Could not compute type of Identifier at /home/runner/work/jupyterlab/jupyterlab/packages/services/src/kernel/messages.ts:135:11
  [2021-06-29 15:21:25] [build-stderr] Could not compute type of Identifier at /home/runner/work/jupyterlab/jupyterlab/packages/services/src/kernel/messages.ts:135:11
  [2021-06-29 15:21:25] [build-stdout] Done extracting /home/runner/work/jupyterlab/jupyterlab/packages/services/src/kernel/manager.ts (110 ms)
  [2021-06-29 15:21:25] [build-stdout] Extracting /home/runner/work/jupyterlab/jupyterlab/packages/services/src/kernel/messages.ts
  [2021-06-29 15:21:25] [build-stdout] Done extracting /home/runner/work/jupyterlab/jupyterlab/packages/services/src/kernel/manager.ts (110 ms)
  [2021-06-29 15:21:25] [build-stdout] Extracting /home/runner/work/jupyterlab/jupyterlab/packages/services/src/kernel/messages.ts
  [2021-06-29 15:21:25] [build-stderr] /opt/hostedtoolcache/CodeQL/0.0.0-20210622/x64/codeql/javascript/tools/typescript-parser-wrapper/node_modules/typescript/lib/typescript.js:65953
  [2021-06-29 15:21:25] [build-stderr]             function getTypeAtFlowNode(flow) {
  [2021-06-29 15:21:25] [build-stderr]                                       ^
  [2021-06-29 15:21:25] [build-stderr] RangeError: Maximum call stack size exceeded

[blink1073]

You're right, it started failing in master and in #10462 as well today.