[FR] allow to "override" registered element

[farfromrefug]

I use my own custom component for buttons, labels,...
So i like to "override" the native element to keep my app clean
Right now it is not possible with svelte-native

svelte-native/src/dom/basicdom/element-registry.ts

Line 13 in b854acd

throw new Error(`Element for ${normalizedName} already registered.`)

Would you be willing to allow it?
May be through an option?

I can make a PR if we decide on the way forward

[halfnelson]

yeah, I don't see why not

[halfnelson]

Merged your PR. Thanks !