WebView communication may be slow on mobile

[FrederikBolding]

snaps/packages/snaps-controllers/src/services/webview/WebViewMessageStream.ts

Lines 68 to 73 in cbe55de

	// To prevent XSS, we base64 encode the message before injecting it.
	// This adds significant performance overhead.
	// TODO: Should we use mobile native base64 here?
	const bytes = stringToBytes(json);
	const base64 = bytesToBase64(bytes);
	this.#webView.injectJavaScript(`window.postMessage('${base64}')`);

[FrederikBolding]

We made progress on this but it may still be slow.