Suggestion: deprecate activeElement

[ollema]

Describe the feature in detail (code, mocks, or screenshots encouraged)

I suggest to deprecate and/or remove the activeElement utility and instead refer to the now builtin activeElement binding on <svelte:document>.

Alternatively, the activeElement could be rewritten to reuse the new builtin binding if you would like to keep it.

What type of pull request would this be?

Enhancement

Provide relevant links or additional information.

sveltejs/svelte#11879

[TGlide]

Runed is meant to work outside of Svelte components as well, so we'll keep the utility, but a note in the docs would be helpful.

[notramo]

@TGlide, could you reopen this? The docs hasn't been updated yet.

Also worth mentioning the read-only focused binding which exists on every Element. It may be a cleaner solution for some use cases.