perf: treat `<img loading>` as a static element again (#18711)

Emits less code and skips two live DOM traversals per instance.

`is_static_element` treats `<img>` with a `loading` attribute as
non-static. That was added in #14237 so `RegularElement` could emit
`$.handle_lazy_img(node_id)`, which needed a reference to the element.
#15272 deleted `handle_lazy_img` (replaced by `importNode`) and removed
the call site, but left this check behind.


---------

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>

.changeset/tidy-owls-repeat.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+perf: treat `<img loading>` as a static element again

packages/svelte/src/compiler/phases/3-transform/client/visitors/shared/fragment.js

@@ -171,11 +171,6 @@ export function is_static_element(node) {
 			return false;
 		}
 
-		// We need to apply src and loading after appending the img to the DOM for lazy loading to work
-		if (node.name === 'img' && attribute.name === 'loading') {
-			return false;
-		}
-
 		if (attribute.value !== true && !is_text_attribute(attribute)) {
 			return false;
 		}

packages/svelte/tests/snapshot/samples/skip-static-subtree/_expected/client/index.svelte.js

@@ -40,10 +40,7 @@ export default function Skip_static_subtree($$anchor, $$props) {
 
 	option.value = option.__value = 'a';
 	$.reset(select);
-
-	var img = $.sibling(select, 2);
-
-	$.next(2);
+	$.next(4);
 	$.template_effect(() => $.set_text(text, $$props.title));
 	$.append($$anchor, fragment);
 }