Add utf16 to JSI

[TatianaKapos]

Problem Description

Recent integration brings in facebook/react-native#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: facebook/react-native#47331 and facebook/react-native#47422

Link to the integration where the error originated

#14167

Link to commit

facebook/react-native#47356
facebook/react-native#47331
facebook/react-native#47422

Forked files

1. testlib.cpp

Upstream PR

No response

Build Configuration

None

[TatianaKapos]

Moving to 0.78, not blocking for 0.77. Hermes runs with the new changes but will fails if you try to use utf16

[anupriya13]

#14650