Add feature for Rewriter API

[reillyeon]

Specification

https://webmachinelearning.github.io/writing-assistance-apis/#rewriter-api

Description

The rewriter API uses generative AI to transform and rephrase input text in the requested ways.

Documentation

https://developer.chrome.com/docs/ai/rewriter-api

Browser support

Active Origin Trials in Google Chrome and Microsoft Edge.