utf8 OpenHarmony Adaptation Proposal

## Background

OpenHarmony is an open-source operating system and community that is widely used in the field of intelligent terminals.

Currently,utf8 is widely used in mobile application development for OpenHarmony. We have created this Issue hoping to supplement the guidance on using utf8 in the OpenHarmony system in the upstream repository.

## Adaptation Plan

We have completed the adaptation of utf8 for OpenHarmony. The specific details are as follows:

- A [demo](https://gitcode.com/openharmony-tpc/openharmony_tpc_samples/tree/master/utf8) demonstrating the use of utf8 in OpenHarmony is provided.
- In accordance with the OHPM (OpenHarmony Package Manager) specification, the adapted version has been released to the OpenHarmony [Third-Party Software Package Center](https://ohpm.openharmony.cn/#/en/detail/utf8).

We will submit the adaptation code via a PR as soon as possible.

## Tests

We have carried out comprehensive and in-depth compatibility tests for different versions of OpenHarmony and various types of OpenHarmony devices.

Verification has been passed on the following versions:

- DevEco Studio: 4.0 Canary2 (4.0.1.300); SDK: API10(4.0.9.6)

The test results show that MetaPhone has excellent compatibility with OpenHarmony, and there are no obvious stability issues. If necessary, we can provide detailed test reports at any time.

## Tags

Enhanced Functionality, Compatibility, Cross-Platform

Start by reviewing the linked OpenHarmony demo and OHPM package entry, then compare them with the utf8.js repository. The issue says an adaptation PR will follow; completion depends on that PR defining the upstream changes and documentation needed for OpenHarmony support.

Written by the indexing model from the issue text.