Avoid re-registering bslib components and globals

[gadenbuie]

Fixes #1044

Avoids redefining bslib-provided custom elements or web components (e.g. bslib-tooltip, bslib-popover) as well as globally-registered classes (bslib.Sidebar and bslib.Card).

In both cases a console error message is provided:

[bslib] Global window.bslib.Sidebar was already defined, using previous definition.
[bslib] Custom element bslib-tooltip was already defined, using previous definition.

[cpsievert]

I'd be curious to know how registerBinding() handles this (i.e., does the last one win)? Seems like it'd be wise to match whatever it does?

[gadenbuie]

Would we want adding bslib::value_box() to a Quarto dashboard to use Quarto's components -- that they test against and expect to work -- or to use bslib's component js instead?

[cpsievert]

Ah, good point, makes sense for the 1st one to win then. But also, if the last one wins for registerBinding(), wouldn't the binding be using the wrong Sidebar (i.e., we should maybe update registerBinding() to do something similar to registerBslibGlobal())?

[gadenbuie]

registerBinding() is basically a safe call to BindingsRegistry.register() in shiny. "registering" a binding just adds it to the end of an array. The .getBindings() method breaks ties using the priority propery, followed by most-recently-registered.

Anyway, you're pointing out that this isn't an unambiguous or complete fix, and I agree. This PR at least gets us out of the position of breaking Dashboards. We'll have to do some thinking in the future