UTF-8 Encoded Emojis render as missing characters

### Bug Description On macos, emojis no longer render when encoded in utf-8. I am unsure if this is the case for other encodings but they do not render in shared string. ### Reproducible Code (if applicable) ```slint ``` ### Environment Details - Slint Version: v1.17 - Platform/OS: Mac - Programming Language: Rust - Backend/Renderer: Skia ### Product Impact _No response_