feat: De-duplicate client console messages

[gadenbuie]

Seen in rstudio/bslib#1159. It's possible for bindAll() to be called in a way that we repeatedly issue the same warnings/errors for duplicate or repeated IDs.

This PR updates the shiny-error-console component to de-duplicate message when new messages are added to the console.

Before	After

[jcheng5]

I'm fine with this PR's behavior as-is, but if the error console becomes more general in the future we should have a duplicate count like JS consoles have.

[gadenbuie]

but if the error console becomes more general in the future we should have a duplicate count like JS consoles have.

I agree and would like this too. As it is now, however, there's very little added value in showing message counts. It's more likely that we'd emit multiple messages signaling one problem than have multiple problems emit identical messages. The good news is that we still emit all messages to the browser console, where the call stack can help differentiate.

If we make the console more general (which I'd like to see), we'll have to revisit this whole code path and I doubt we'll forget about adding message counts.