fix: Handle unicode in webview events.

[tdomhan]

The request header does not support unicode characters leading to Type: error when calling setRequestHeader with a non-ascii string. This PR first encodes the data using base64 before setting the header. The downside is that this increases the content size by 33%.

This addresses https://github.com/DioxusLabs/dioxus/issues/3125

Running the build updates all Javascript files. I assume this is due to the Typescript version. I'm using 5.7.2. Let me know if I should be using a specific version.