[whatwg/dom] Set registry on null registry element on adopt instead of on insert (PR #1423)

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In order to support scenarios for elements with a null custom element registry without shadow DOM, we decided to modify the behavior when it comes to setting registry on null registry element. By setting the registry on adopt instead of on insert allows us to have null registry element in light DOM while being backwards-compatible.

Fixes #1413 partially. There are two more spec changes expected to add element attribute and allow null registry option during element creation and shadow attachment as mentioned in https://github.com/whatwg/dom/issues/1413#issuecomment-3530198733



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You can view, comment on, or merge this pull request online at:

  https://github.com/whatwg/dom/pull/1423

-- Commit Summary --

  * Remove registry restoration on insert but do it in adopt

-- File Changes --

    M dom.bs (33)

-- Patch Links --

https://github.com/whatwg/dom/pull/1423.patch
https://github.com/whatwg/dom/pull/1423.diff

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