Provide user feedback when creating a shinylive link for a dir with several files takes a while

[karangattu]

When the user creates a shinylive link for a directory with several files, for e.g. https://github.com/posit-dev/py-shiny/tree/main/examples/brownian, the user gets to select the editor or app mode in Shinylive mode, but the corresponding modal that asks the user to select the option to either open the link or copy the link takes a while.

We should have a way to provide user feedback during this waiting period, so that the user knows that the operation is still in progress.

[gadenbuie]

@karangattu the hard part here is that this example is very much an edge case. It likely takes as long as it does because the app is far too big to be sent to shinylive.io -- in this case generally because there is a node_modules folder in the example with lots of files.

The experience of having a progress indication show up is definitely better when it takes this long, but we can't differentiate between long and short URL encoding times. As a result, we'd end up always showing a progress toast even when it's nearly instantaneous.

I think the fix we might want to implement here is to detect that the app bundle is too big to compress into a URL, but I'm also not sure where that line would be.