Update Markdown elements even if invisible (e.g. inside tooltip or tab)

[me21]

This is an attempt to fix #2779. It seems to make Markdown elements update correctly but breaks Mermaid diagrams in Markdown elements, not sure why.
Additional changes are welcome.

[me21]

Mermaid diagrams work now.

[me21]

There is an annoying blinking during the update of the content if Mermaid diagram is shown. However, this bug is not so major, I think, and Markdown elements now are correctly shown in tooltips :)

[me21]

I'm sorry, I force-pushed new fix - it appears to be a one-liner 😄
But it introduces blinking of visible content on every update if Mermaid diagram is displayed inside Markdown element.

[falkoschindler]

Wow, that's a nice solution!
I just can't reproduce the blinking - or I don't know where to look. Do you have some example code to reproduce it?

[me21]

The following minimal example reproduces blinking for me:

textarea = ui.textarea()
markdown = ui.markdown(extras=['fenced-code-blocks', 'tables', 'mermaid'])
markdown.bind_content_from(textarea, 'value')

Now type the following into textarea:

```mermaid
graph LR;
    A-->B;
    A-->C;
```

You should see Mermaid diagram in Markdown. Now type something in textarea below that code block. You will see that markdown contents on each change will shortly blink with the code of the Mermaid diagram before being replaced with the diagram itself.

[falkoschindler]

I think I found a rather nice solution: Instead of calling the "update" method with an HTML payload, we can simply update the element and handle the "updated" lifecycle hook on the client to render Mermaid diagrams.

I tested with the following snippet

with ui.textarea() as textarea:
    with ui.tooltip():
        ui.markdown(extras=['fenced-code-blocks', 'mermaid']).bind_content_from(textarea, 'value')

ui.markdown(extras=['fenced-code-blocks', 'mermaid']).bind_content_from(textarea, 'value')

as well as with the code from #278 (comment). All seems to work well. @me21 Would you like to try it out?

[me21]

@falkoschindler works nicely!

[falkoschindler]

Great! Thank you for your contribution, @me21! I think together we found a really nice solution to this rendering problem. 🙂