Run adopt as part of insert

[pshaughn]

Changes of whatwg/dom#754 are reflected, but we mostly aren't passing the associated tests. In many cases this is because we don't actually have the shadow DOM functionality that makes this behavior relevant, but that's not all that's being tested and there is probably some other missing piece.

It might make sense to merge this (assuming it passes CI) and open another issue investigating the failures?

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fulfill the letter of Run adopt as part of insert #25265 but aren't passing all the associated tests

• There are tests for these changes

[highfive]

Heads up! This PR modifies the following files:

• @asajeffrey: components/script/dom/document.rs, components/script/dom/shadowroot.rs, components/script/dom/node.rs, components/script/dom/documentfragment.rs, components/script/dom/htmltemplateelement.rs
• @KiChjang: components/script/dom/document.rs, components/script/dom/shadowroot.rs, components/script/dom/node.rs, components/script/dom/documentfragment.rs, components/script/dom/htmltemplateelement.rs

[highfive]

Warning

• These commits modify unsafe code. Please review it carefully!

[jdm]

I went to open a spec issue about this and found whatwg/dom#813.

[jdm]

Given whatwg/dom#813 (comment), perhaps we should hold off on this work until it settles in spec land.

[pshaughn]

That makes sense.

[pshaughn]

whatwg/dom#819 hasn't landed yet but whatwg/dom#813 is still unresolved, so if adopt is going to be moved, it will probably be in a different enough way to require completely different code changes.