Custom element syntax

[whitphx]

Found that the JS-based syntax has one clear downside that developers have to take care of escaping some characters such as backtick (`) and backslash (\).
Ref:

stlite/packages/sharing-editor/src/export/html.ts

Lines 13 to 18 in db36554

	export function escapeTextForJsTemplateLiteral(text: string): string {
	return text
	.replaceAll("\\", "\\\\")
	.replaceAll("`", "\\`")
	.replaceAll("${", "\\${");
	}

Custom element syntax like below allows developers to write the Python code without such cares.

<stlite-app>
import streamlit as st

st.write("Hello World")
</stlite-app>