This PR adds framework support for the Search Web feature in iOS. 

https://github.com/flutter/flutter/assets/36148254/c159f0d9-8f14-45e7-b295-e065b0826fab

The corresponding merged engine PR can be found [here](https://github.com/flutter/engine/pull/43324).
This PR addresses https://github.com/flutter/flutter/issues/82907 
More details are available in this [design doc](https://docs.google.com/document/d/1QizXwBiO-2REIcEovl5pK06BaLPOWYmNwOE5jactJZA/edit?resourcekey=0-1pb9mJiAq29Gesmt25GAug)