Webview: shows a "Not implemented" warning when triggering search

[bpasero]

I think this is not very useful and I can still search using the browser and things get revealed so I suggest to not show this notification.

Related: #96307

[bpasero]

//cc @rzhao271

[bpasero]

After having played with dev/mjbvz/iframe-search and seeing the changes there, here are some thoughts for pushing this forward:

• IFrameWebview as base class of all could own the WebviewFindWidget and provide it for the web and desktop cases
• implementation for desktop leverages @rzhao271 work with the new Electron support for finding in iframe
• implementation on web leverages window.find API which I verified actually works in Chrome, Firefox and Safari reasonably well [1]

I was about to prototype this for web, but fail to understand how the iframe preload script gets provided from a CDN it seems. In order to make window.find work the preload script needs to provide a hook (via postMessage?) to run it.

[1]

• you can find next / find previous
• find results are highlighted using selection (same as native find)
• there does not seem to be a way to highlight all results initially
• I did not find a way to theme the find selection color, so it appears like the normal text selection color