use document.importNode for when img/iframe use loading="lazy"

[titoBouzout]

This attempts to reuse the same logic as hasCustomElement as an isImportNode. That currently only becomes true when an image/iframe has the attribute loading="lazy"

To solve solidjs/solid#1828 avoiding using document.importNode for every other element.

This in theory should have worked on the first try. For some reason nested elements with such an attribute won't be marked as isImportNode. Handled this oddity with a least resort regexp for now.

_$template('<img src=""loading=lazy>', true, false),
_$template('<div><img src=""loading=lazy>', true, false);

Without the regexp the last one won't have true, false)

[titoBouzout]

ok, this is ready for review. I was able to get rid of the regexp.

--
I had the issue(now fixed) of the following nested template not having the "use importNode" bit
_$template('<div><img src=""loading=lazy>');

I presume because the condition child.id didnt enter. So I moved the copy of the flag above it, and that worked. Now I wonder if theres some latent bug of hasHydratableEvent and hasCustomElement suffering the same problem. That child templates do not copy some properties to its parents

[ryansolid]

It's a bit odd. What I mean is every native element will have child.id I'd think. But maybe I'm wrong. Maybe only ones with dynamic bindings or something.