Add script_to_iframe function

[MarcSkovMadsen]

Sometimes you would like to embed a app pyodide/ pyscript app in another html document. And maybe you don't want or cannot host the panel convert assets externally.

One use case is plugins/ filters/ extension to document frameworks like Sphinx, mkDocs or Quarto.

Here you would need code like the below

import html
from io import StringIO
import sys  

from panel.io.convert import script_to_html
from panel.io.resources import set_resource_mode

ALLOW="accelerometer;autoplay;camera;document-domain;encrypted-media;fullscreen;gamepad;geolocation;gyroscope;layout-animations;legacy-image-formats;microphone;oversized-images;payment;publickey-credentials-get;speaker-selection;sync-xhr;unoptimized-images;unsized-media;screen-wake-lock;web-share;xr-spatial-tracking"

def script_to_iframe(code: str, runtime: str="pyscript")->str:
    """Converts the code to a valid iframe for embedding"""
    if runtime=="pyodide-worker":
        # The pyodide-worker runtime generates an both a html and a js file
        raise ValueError("pyodide-worker runtime is not supported!")
    with set_resource_mode('cdn'):
        ht, _ = script_to_html( 
            StringIO(script), runtime=runtime
        )
    ht = html.escape(ht)
    return f"""<iframe frameborder="0" srcdoc="{ht}" class="panel-app" onload="resizePanelApp(this)" allow="{ALLOW}"></iframe>"""

Its tedious to have to develop and maintain this in many settings.

It would be nice if Panel included a ready to use script_to_iframe function.

Additional Context

• the pyodide-worker is not supported by the above implementation. The external js worker would need to be hosted externally by panel (without the code) or embedded in the html document generated via a blob url. See https://gist.github.com/nolanlawson/23eff93d27ad09ff44b7e4d56ffd1d54. The pyoide-worker runtime loading looks much nicer than the pyscript loading. Thus I would prefer to be able to use that one.
• The limitation of the script_to_iframe is that it does not work well if you want to embed many panel apps in a page because each iframe loads all the resources etc. Shiny-live solves this by loading once outside the iframe and then setting up a communication channel between parent window and iframe.
• I think the line with set_resource_mode('cdn') is a hack and some refactoring of Panel code should be done so that this can be avoided.