Set custom element data fails when using builtin custom elements. #16591
Description
Describe the bug
The helper set_custom_element_data only checks for autonomous custom elements but fails to check for builtin custom elements (is attribute) here, so it always set the value as attribute.
Reproduction
https://svelte.dev/playground/46f14880c73443318e26dd375ff3c0d2
Logs
System Info
REPLSeverity
annoyance