Don't use `type_of` to determine if item has intrinsic shim
When we're calling `resolve_instance` on an inline const, we were previously looking at the `type_of` for that const, seeing that it was an `extern "intrinsic"` fn def, and treating it as if we were computing the instance of that intrinsic itself. This is incorrect.
Instead, we should be using the def-id of the item we're computing to determine if it's an intrinsic.
Fixes#114660
a87dda3b3d