Add utf16 to JSI

Problem Description

Recent integration brings in https://github.com/facebook/react-native/pull/47356 which we need to update the JSI files in our repo and Hermes-windows repo to add utf16 method. Since this isn't being used in any code yet, I was able to just disable to test to get the integration building!

There were also these two PRs in the integration that may need to be pulled into the hermes-repo: https://github.com/facebook/react-native/pull/47331 and https://github.com/facebook/react-native/pull/47422

Link to the integration where the error originated

https://github.com/microsoft/react-native-windows/pull/14167

Link to commit

https://github.com/facebook/react-native/pull/47356
https://github.com/facebook/react-native/pull/47331
https://github.com/facebook/react-native/pull/47422

Forked files

1. testlib.cpp

Upstream PR

No response

Build Configuration

None