Write string value into Utf16 string buffer

CHAKRA_API    JsCopyStringUtf16(        _In_ JsValueRef value,        _In_ int start,        _In_ int length,        _Out_opt_ uint16_t* buffer,        _Out_opt_ size_t* written);

• value: JavascriptString value
• start: Start offset of buffer
• length: Length to be written
• buffer: Pointer to buffer
• written: Total number of characters written

The codeJsNoError if the operation succeeded, a failure code otherwise.

This API is experimental and may have breaking change later.

When size of thebuffer is unknown,buffer argument can be nullptr.In that case,written argument will return the length needed.

When start is out of range or < 0, returns JsErrorInvalidArgumentandwritten will be equal to 0. If calculated length is 0 (It can be due to string length orstartand length combination), thenwritten will be equal to 0 and callreturns JsNoError.