[Blazor] Get rid of special webassembly behavior in the static web assets SDK #59468
Description
In particular, we allow defining assets with an ItemSpec that points to a location that doesn't exist, and we have logic all over the place to fallback on the original item spec. That is not only costly, but error prone.
Recently, a bug was discovered that was caused because we didn't account for this ItemSpec behavior.
We should define webassembly assets properly and get rid of this problematic behavior on the SDK