fix(Chat): ui.Chat() should never scroll a parent element of the chat container element

[cpsievert]

Discovered via posit-dev/shinychat#42

Here is a minimal Python equivalent reprex. Note that, on load, the page scrolls down past the chat container. It shouldn't scroll at all.

from shiny.express import ui

chat = ui.Chat(
    id="chat",
    messages=[
        (
            "Hello! How can I help you today?\n\n"
            "Hello! How can I help you today?\n\n"
            "Hello! How can I help you today?\n\n"
            "Hello! How can I help you today?\n\n"
            "Hello! How can I help you today?\n\n"
            "Hello! How can I help you today?\n\n"
        )
    ],
)

with ui.card():
    chat.ui()

ui.div(style="height:3000px")

[gadenbuie]

Looks good! Just one more nitpick on top of Copilot's suggested change

[gadenbuie]

This doesn't completely solve the problem. I think it fixed the issue for the reprex app because the card scrolls, but when the card doesn't scroll the parent container still scrolls. I.e. changing out page_fluid() for Shiny Express's default page_fillable() still exhibits the problem.

[gadenbuie]

Turns out el.TagName returns SHINY-CHAT-MESSAGES (at least on Chrome). Fix incoming.