Svelte 5 support

[madeleineostoja]

Any plans to more fully support Svelte 5 now that's in release candidate?

The most notable change to bring svelte-file-dropzone in line with deprecations etc would just be to replace events (on:drag etc) with callbacks (ondrag etc).

I've also noticed that many svelte-file-dropzone props aren't properly reactive when I use it in a Svelte 5 (runes mode) environment. I haven't dug too far into it yet, but my first guess from a quick skim of the codebase is how events are composed.