Make `files` work both ways?

[brunnerh]

Describe the problem

In Svelte 4 the input binding for files is one-way out of the element.
This is unexpected behavior because the property can be set

Relates to:

• Svelte 5: 'files' is not a valid binding #9418
• fix: add missing files binding #9415

Describe the proposed solution

If the user wants to set the property, they will just have to deal with the DataTransfer shenanigans mentioned in #9415 themselves until maybe a different way to construct a FileList is standardized.

Since this is a small breaking change, Svelte 5 would be a good candidate in my opinion.

Alternatives considered

-

Importance

nice to have

[teemingc]

Related to #8316 and #9080 which will need to be adapted for svelte 5

Svelte 5 reproduction. Clicking the reset button doesn't reset the files.