Follow-up from [this discussion](https://github.com/angular/angular/pull/33419#discussion_r339296216). In Ivy we don't use the schema to validate tag names, but instead we use feature detection to figure out whether an element is supported. While this should generally be more accurate, it'll also end up throwing for some more innocent cases. E.g. now Ivy throws an error for `main` elements in IE which is accurate since IE doesn't support the element, but is annoying since there is no functionality attached.
These changes switch to logging a warning instead, similarly to what we're doing for unknown properties.
PR Close#34524
6fda7f3da4