Migrate to CSS Custom Highlight API for search results

[krassowski]

Problem

JupyterLab highlights search matches in code and outputs by modifying the DOM. This is:

• slow because it can triggers layout/style computation
• error-prone, especially when the output gets copied and pasted elsewhere, for example see Copy Output to Clipboard does not include (hides?) search matches #15280

Proposed Solution

CSS Custom Highlight API is the preferred way of achieving highlighting of results; there is a dedicated example on MDN.

Additional context

As of the day of writing the browser support is not yet there, but Firefox Nightly recently enabled it so it will likely ship.

• Chrome: 102+
• Edge: 102+
• Firefox: Nightly
• Opera: 91
• Safari: nope

[krassowski]

Safari supports this API since 17.2