CTRL+F/CMD+F overrides browser's Find function with custom code

[JasonWeill]

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Description

When the user presses CTRL+F or CMD+F, custom JupyterLab code for Find appears. This behavior differs from the classic notebook (https://github.com/jupyter/nbclassic/) which does not override these shortcut keys, and which instead allows the browser's built-in search bar to be displayed and used.

Expected behavior

By default, in Notebook 7, CTRL+F or CMD+F should cause the browser's default search user interface to display.

Context

This was spun off from #7041, originally filed by @jph00.

Jupyter Notebook should not override browsers' built-in keyboard shortcuts, wherever possible.

Virtual rendering may cause the browser's search box to search only a portion of the notebook; unrendered cells may not be made available to the browser.