Bug 290396

## Explanation In Desktop Safari 17.5 and 18.3.1 and iOS Safari 18.3.2 (only tested versions so far) a form control rendered inside a declarative shadow DOM leak into the host element's form. This does not happen in Firefox 136 or Chrome 134. Essentially when you have the following: <form> <x-element> <template shadowrootmode="open"> <input name="foo" value="bar"> </template> </x-element> </form> the FormData you will get the following: formData.getAll("foo") // => ["bar"] only in Safari. In Firefox and Chrome you will get an empty array. In addition, doing `form.elements` returns form controls from the shadow dom in Safari. This does not happen when the shadow dom is client side rendered *only* when its rendered via Declarative Shadow DOM. This feels like unintended and unexpected behavior. https://codepen.io/paramagicdev/pen/gbOjxJy ^ reproduction